Organic Loading Rate

The anaerobic digestion of glycerol derived from biodiesel manufacturing, in which COD was found to be 1010 g/kg, was studied in batch laboratory-scale reactors at mesophilic temperature using granular and non-granular sludge. Due to the high KOH concentration of this by-product, H 3 PO 4 was added to recover this alkaline catalyst as agricultural fertilizer (potassium phosphates). Although it would not be economically viable, a volume of glycerol was distilled and utilised as reference substrate. The anaerobic revalorisation of glycerol using granular sludge achieved a biodegradability of around 100%, while the methane yield coefficient was 0.306 m 3 CH 4 /kg acidified glycerol. Anaerobic digestion could be a good option for revalorising this available, impure and low priced by-product derived from the surplus of biodiesel companies. The organic loading rate studied was 0.21-0.38 g COD/g VSS d, although an inhibition phenomenon was observed at the highest load.

Anaerobic digestion is an appropriate technique for the treatment of sludge before final disposal and it is employed worldwide as the oldest and most important process for sludge stabilization. In general, mesophilic anaerobic digestion of sewage sludge is more widely used compared to thermophilic digestion. Furthermore, thermal pre-treatment is suitable for the improvement of stabilization, enhancement of dewatering of the

The performance of mesophilic anaerobic digesters of four large Italian wastewater treatment plants without primary sedimentation were studied. Only the waste activated sludge is stabilised by means of the mesophilic (35-37 8C) anaerobic digestion process. The anaerobic digesters generally worked with a hydraulic retention time in a range of 20-40 days and an organic loading rate of some 1 kg VS/m 3 reactor day. The solids content of the sludge fed to the digesters was in the range 2.6-3.9% and the gas produced per kilogram of volatile solids added was in the range 0.07-0.18 m 3 /kg VS fed . The specific gas production per kilogram of volatile solids destroyed was in the range 0.5-0.9 m 3 / kg VS destroyed and the reduction of the volatile solids concentration was in the range 13-27% (average 18%). These figures are particularly significant when designing anaerobic digesters for the treatment of waste activated sludge as single substrate. Moreover, it was observed that the higher the applied solid retention time in the activated sludge process for wastewater treatment, the lower the gas production. In particular, the specific gas production decreased from 0.18 to 0.07 m 3 /kg VS fed when increasing the solid retention time in the wastewater treatment line from 8 to 35 days. Finally, a mathematical model for the prediction of biogas production on the solid retention time applied in the wastewater treatment process was developed. #

The anaerobic digestion of solid wastes is now a widely-used technology in Europe with more than 50 full-scale plants operating. However, anaerobic solid waste digestion is still used to only a limited extent in North America with only three facilities in Canada. Because of the expected importance of anaerobic digestion in the future for energy recovery, reliable tools are required to evaluate the different available technologies, as well as the feed stocks that are suitable for treatment. Therefore, this paper presents a framework that has been developed for evaluating anaerobic solid waste digestion. To develop the framework, a review of the performance of digestion processes was first conducted. Because the data presented were for very different operational parameters (retention time, temperature, configuration set up, mixing, etc.) as well as substrates used for digestion, a standard method of comparison was developed. Gas production per Mg input, organic loading rate and percent volatile solids removal were identified as useful standard parameters for evaluating the performance of different technologies. This framework was constructed as a spread sheet and can be used for different set ups (configuration, organic loading rate, etc.) and with different substrates. It can predict, based on the input and using mass balances, the mass of products of the digester including biogas, treated solids and water. This framework provides a useful tool for evaluating the technical capabilities of different technologies, predicting the quantity of the products, and ultimately, making decisions as to which technologies best meet local needs.

AbstractÐA mixed culture bio®lm was developed with a sulfur oxidising, heterotrophic bacterium Thiosphaera pantotropha, autotrophic nitri®ers and other heterotrophs in a three stage rotating biological contactor (RBC). Speci®c bene®ts due to peculiar properties of T. pantotropha of simultaneous heterotrophic nitri®cation and aerobic denitri®cation were derived in the reactor investigated for a combined carbon and nitrogen removal from a synthetic domestic sewage. The ®rst stage bio®lm which contained T. pantotropha showed high COD and NH 4 + -N removal rates of 5.8±14.1 g COD/m 3 Ád and 0.47±1.1 g N/m 2 Ád for the corresponding loading rates of 6.9±20.7 g COD/m 3 Ád and 0.69±2.09 g N/m 2 Ád, respectively. Contrary to the conventional units designed for a concurrent carbon removal and nitri®cation, the nitri®cation rates increased linearly with an increase in organic loading rate before stabilising at about 1 g N/m 2 Ád corresponding to a COD loading rate of about 15 g/m 2 Ád and a nitrogen loading rate of 1.5 g N/m 2 Ád showing a change in the order of reaction from ®rst to zero. A simultaneous nitrogen removal of 20±68% was also obtained. The system's performance indicated that a single stage aerobic bio®lm can be developed to meet the increasingly stringent regulations on euent nitrogen discharges aording several advantages over the conventional systems, e.g. low buer requirements, no need for external carbon source for denitri®cation, etc., which may result in substantial reduction in the treatment cost. #

The results presented in this paper are from studies on a laboratory-scale upflow anaerobic sludge blanket (UASB) reactor and an anaerobic packed-bed (APB) reactor treating potato leachate at increasing organic loading rates from 1.5 to 7.0 g COD/1/day. The hydraulic retention times ranged from 13.2 to 2.8 days for both reactors during the 100 days of the experiment. The maximum organic loading rates possible in the laboratory-scale UASB and APB reactors for stable operation were approximately 6.1 and 4.7 g COD/l day, respectively. The COD removal efficiencies of both reactors were greater than 90% based on the total COD of the effluent. The methane yield increased with increasing organic loading rate up to 0.23 l CH 4 /g COD degraded in the UASB reactor and 0.161 CH 4 /g COD degraded in the APB reactor. The UASB could be run at a higher organic loading rate than the APB reactor and achieved a higher methane yield. Signs of reactor instability were decreasing partial alkalinity and pH and increasing amounts of volatile fatty acids. The study demonstrated the suitability of the UASB and a packed-bed reactor for treating leachate from potato waste. q

Co-digestion of rendering and slaughterhouse wastes was studied in laboratory scale semi-continuously fed continuously stirred tank reactors (CSTRs) at 35 and 55°C. All in all, 10 different rendering plant and slaughterhouse waste fractions were characterised showing high contents of lipids and proteins, and methane potentials of 262-572 dm 3 CH 4 /kg volatile solids (VS) added . In mesophilic CSTR methane yields of ca 720 dm 3 CH 4 /kg VS fed were obtained with organic loading rates (OLR) of 1.0 and 1.5 kg VS/m 3 d, and hydraulic retention time (HRT) of 50 d. For thermophilic process, the lowest studied OLR of 1.5 kg VS/m 3 d, turned to be unstable after operation of 1.5 HRT, due to accumulating ammonia, volatile fatty acids (VFAs) and probably also long chain fatty acids (LCFAs). In conclusion, mesophilic process was found to be more feasible for co-digestion than thermophilic process, methane yields being higher and process more stable in mesophilic conditions.

In this paper, bioaugmentation was applied to upgrade a full-scale activated sludge system (S2) into a contact oxidation system (S1). Results showed that when chemical oxygen demand (COD) and ammonia nitrogen (NH þ 4 -N) concentration of the petrochemical wastewater were 320-530 mg/L and 8-25 mg/L, respectively, the bioaugmented process (S1) took only 20 days when they were below 80 mg/L and 10 mg/L, respectively. However, the unbioaugmented conventional activated sludge process (S2) spent 30 days to reach the similar effluent quality. As the organic loading rate (OLR) increased from 0.6 to 0.9 and finally up to 1.10 kg COD/m 3 d, S1 showed strong resistance to shock loadings and restored after three days compared to the seven days required by S2. Based on the results of this paper, it shows that bioaugementation application is feasible and efficient for the process upgrade due to the availability of the bioaugmented specialized consortia.

In this study, the optimum operating conditions of a lab-scale completely stirred acidogenic reactor treating a chemical synthesis-based pharmaceutical wastewater were determined. Individual effects of hydraulic retention time (HRT), organic loading rate (OLR) and pH on the degree of acidification were investigated at a mesophilic temperature (35 AE 1 8C), for HRT in the range 8-24 h, OLR up to 14 kg COD/m 3 d and pH in the range of 5.0-6.3. A maximum acidification level of 44% and COD removal efficiency of 13%, were obtained at an OLR of 13 kg COD/m 3 d at pH of 5.5 AE 0.1 with an HRT of 12 h. Under these conditions, acetic, propionic and n-butyric acids were found to be predominant volatile fatty acids in the acidogenic reactor. #

A sequencing batch reactor (SBR) has certain advantages over conventional activated sludge processes (ASP) for the treatment of complex wastewater. The performance of a sequencing batch reactor in treating complex chemical effluents was investigated with a suspended biomass configuration and operating under aerobic conditions. A total sequence of 24 h (15 min: filling phase; 23 h: reaction phase (aeration with recirculation); 30 min: setting; and 15 min: withdrawal) was employed and studied with various organic loading rates (1.0 kg COD/m3/day: 1.7 kg COD/m3/day and 3.5 kg COD/m3/day). The SBR performance was assessed by means of carbon removal and operational parameters such as pH, oxidation–reduction potential (ORP), sludge volume (SV), sludge volume index (SVI), suspended solids (SS) and volatile suspended solids (VSS), which were monitored during reactor operation. The SBR showed relatively more efficient performance over conventional suspended growth systems. About 8% sulphate was removed under anoxic conditions at all the studied organic loading rates. Enhanced performance with SBR over conventional ASP may be due to enforced short term unsteady state conditions coupled with periodic exposure of the microorganisms (physiological state) to defined process conditions which facilitate the required metabolic conditions for treating complex chemical effluents.

Two types of non-axenic algal cultures, one dominated by the freshwater microalgae Scenedesmus obliquus and the other by the marine microalgae Phaeodactylum tricornutum, were cultivated in two types of simple photobioreactor systems. The production rates, expressed on dry matter (DM) basis, were in the order of 0.12 and 0.18 g DM L À1 d À1 for S. obliquus and P. tricornutum respectively. The biogas potential of algal biomass was assessed by performing standardized batch digestion as well as digestion in a hybrid flow-through reactor (combining a sludge blanket and a carrier bed), the latter under mesophilic and thermophilic conditions. Biomethane potential assays revealed the ultimate methane yield (B 0 ) of P. tricornutum biomass to be about a factor of 1.5 higher than that of S. obliquus biomass, i.e. 0.36 and 0.24 L CH 4 g À1 volatile solids (VS) added respectively. For S. obliquus biomass, the hybrid flow-through reactor tests operated at volumetric organic loading rate (Bv) of 2.8 gVS L À1 d À1 indicated low conversion efficiencies ranging between 26-31% at a hydraulic retention time (HRT) of 2.2 days for mesophilic and thermophilic conditions respectively. When digesting P. tricornutum at a Bv of 1.9 gVS L À1 d À1 at either mesophilic or thermophilic conditions and at an HRT of 2.2 days, an overall conversion efficiency of about 50% was obtained. This work indicated that the hydrolysis of the algae cells is limiting the anaerobic processing of intensively grown S. obliquus and P. tricornutum biomass.

This work aimed to study the treatment of wastewater generated from fruit juice industry (24-30 m 3 /batch). Three treatment schemes have been investigated. The first treatment scheme was a batch activated sludge (AS) system and was operated at different aeration time up to 48 h. The second scheme was two-stage upflow anaerobic sponge reactors (UASRs). Two-stage UASRs were operated at a total hydraulic retention time (HRT) of 13 h corresponding to an organic loading rate (OLR) of 8.7 kg COD/m 3 d. While, the third treatment scheme consisted of a two-stage UASR followed by an AS system which was operated at three different HRTs namely 10, 12, and 14 h. Long term experiments indicated the superiority of the third treatment scheme which operated at a total HRT of 23 h (UASRs: 13 h and AS: 10 h) in terms of chemical oxygen demand (COD), biochemical oxygen demand (BOD 5 ), total suspended solids (TSS) and oil & grease removal. The integrated system achieved an overall removal efficiency of 97.5% for COD, 99.2% for BOD 5 , 94.5% for TSS and 98.9% for oil & grease. The treated wastewater produced from the UASR-AS system complied with the standards set by the Egyptian law regulating the reuse of treated wastewater in agricultural purposes.

We determined the effect of different mixing intensities on the performance, methanogenic population dynamics, and juxtaposition of syntrophic microbes in anaerobic digesters treating cow manure from a dairy farm. Computer automated radioactive particle tracking in conjunction with computational fluid dynamics was performed to quantify the shear levels locally. Four continuously stirred anaerobic digesters were operated at different mixing intensities of 1,500, 500, 250, and 50 revolutions per min (RPM) over a 260-day period at a temperature of 34 AE 18C. Animal manure at a volatile solids (VS) concentration of 50 g/L was fed into the digesters daily at five different organic loading rates between 0.6 and 3.5 g VS/L day. The different mixing intensities had no effect on the biogas production rates and yields at steady-state conditions. A methane yield of 0.241 AE 0.007 L CH 4 /g VS fed was obtained by pooling the data of all four digesters during steady-state periods. However, digester performance was affected negatively by mixing intensity during startup of the digesters, with lower biogas production rates and higher volatile fatty acids concentrations observed for the 1,500-RPM digester. Despite similar methane production yields and rates, the acetoclastic methanogenic populations were different for the high-and lowintensity mixed digesters with Methanosarcina spp. and Methanosaeta concilii as the predominant methanogens, respectively. For all four digesters, epifluorescence microscopy revealed decreasing microbial floc sizes beginning at week 4 and continuing through week 26 after which no microbial flocs remained. This decrease in size, and subsequent loss of microbial flocs did not, however, produce any long-term upsets in digester performance.

The microbial process of converting organic matter into methane and carbon dioxide is so complex that anaerobic digesters have long been treated as "black boxes." Research into this process during the past few decades has gradually unraveled this complexity, but many questions remain. The major biochemical reactions for forming methane by methanogens are largely understood, and evolutionary studies indicate that these microbes are as different from bacteria as they are from plants and animals. In anaerobic digesters, methanogens are at the terminus of a metabolic web, in which the reactions of myriads of other microbes produce a very limited range of compounds--mainly acetate, hydrogen, and formate--on which the methanogens grow and from which they form methane. "Interspecies hydrogen-transfer" and "interspecies formate-transfer" are major mechanisms by which methanogens obtain their substrates and by which volatile fatty acids are degraded. Our understanding of these reactions and other complex interactions among the bacteria involved in anaerobic digestion is only now to the point where anaerobic digesters need no longer be treated as black boxes.

This study investigated the feasibility and the treatment efficiency of a cyclic anoxic/aerobic two-stage MBR for treating polymeric industrial wastewater. The anoxic/aerobic hybrid MBR was operated without sludge withdrawal except sampling during the study. The results showed that the highest COD organic loading rate of 8.7 kg COD/m 3 day from bioreactor was obtained at phase 3. The system achieved 97% BOD 5 and 89% COD removal. It also revealed that 93% of COD removal was contributed by bioreactor at phase 3 and the similar results happened to phases 1 and 2. The highest TN and TKN removals for each phase were 60, 74, 80% and 61, 74, 81%, respectively and limited by nitritation step. SEM images of nascent and fouled membranes were offered to evaluate the cleaning method. The system was operated for 174 days, resulting in high degradation rate, flexibility towards influent fluctuations and limited sludge production.

This work reviews the potential of anaerobic digestion for material recovery and energy production from fruit and vegetable wastes (FVW). These wastes contain 8-18% total solids (TS), with a total volatile solids (VS) content of 86-92%. The organic fraction includes about 75% easy biodegradable matter (sugars and hemicellulose), 9% cellulose and 5% lignin. Anaerobic digestion of FVW was studied under different operating conditions using different types of bioreactors. It permits the conversion of 70-95% of organic matter to methane, with a volumetric organic loading rate (OLR) o f 1-6.8 g versatile solids (VS)/l day. A major limitation of anaerobic digestion of FVW is a rapid acidification of these wastes decreasing the pH in the reactor, and a larger volatile fatty acids production (VFA), which stress and inhibit the activity of methanogenic bacteria. Continuous two-phase systems appear as more highly efficient technologies for anaerobic digestion of FVW. Their greatest advantage lies in the buffering of the organic loading rate taking place in the first stage, allowing a more constant feeding rate of the methanogenic second stage. Using a two-stage system involving a thermophilic liquefaction reactor and a mesophilic anaerobic filter, over 95% volatile solids were converted to methane at a volumetric loading rate of 5.65 g VS/l d. The average methane production yield was about 420 l/kg added VS.

Produced water is a significant waste stream generated in association with oil and gas production. It contains high concentrations of hydrocarbon constituents and different salts. In this study, a membrane sequencing batch reactor (MSBR) was used to treat synthetic and real produced water. The MSBR was evaluated in terms of biodegradation of hydrocarbons in the synthetic produced water with various organic loading rates (OLR) (0.281, 0.563, 1.124, 2.248, and 3.372 kg COD/(m 3 day)), cycle time (12, 24, and 48 h), and membrane performance. The effects of salt concentrations at different total dissolved solids (TDS) (35,000, 50,000, 100,000, 150,000, 200,000, and 250,000 mg/L) on biological treatment of the pollutants in the synthetic and real wastewater were studied. At an OLR of 1.124 kg COD/(m 3 day), an HRT of 48 h and TDS of 35,000 mg/L, removal efficiencies of 97.5%, 97.2%, and 98.9% of COD, total organic carbon (TOC), and oil and grease (O&G), respectively were achieved. For the real produced water, removal rates of 86.2%, 90.8%, and 90% were obtained for the same conditions. However, with increasing salt content, the COD-removal efficiencies of the synthetic and real produced water were reduced to 90.4% and 17.7%, respectively at the highest TDS.

Sago industry is one of the major small-scale sectors in India and over 800 units are located in the southern State of Tamilnadu. Processing of sago generates enormous quantities of high strength wastewater requiring systematic treatment prior to disposal. The present study is an attempt to treat the sago wastewater using Hybrid Upflow Anaerobic Sludge Blanket (HUASB) reactor, which offers the advantages of both fixed film and up flow anaerobic sludge blanket treatment. HUASB reactor with a volume of 5.6 L was operated at Organic Loading Rates varying from 10.7 to 24.7 kg COD/m 3 .day. After 130 days of startup, the reactor produced appreciable decrease in COD of wastewater and removed solids efficiently. The COD removal varied from 91-87%. While the removal of Total Solids was in the range of 61-57%, that of volatile solids varied from 70-67%. The ideal OLR for the reactor was 23.5 kg COD/m 3 .day. The findings of the study open up newer possibilities of design low cost and compact onsite treatment systems with very short retention periods.

Treatment of a low strength complex wastewater of chemical oxygen demand (COD) around 500 mg/L was studied in a 10 L capacity laboratory scale anaerobic baffled reactor (ABR). It was operated at hydraulic retention times (HRTs) of 20, 15, 10, 8 and 6 h. Corresponding organic loading rates (OLRs) were 0.6, 0.8, 1.2, 1.5 and 2 kg COD/m 3 d. At every HRT (or OLR), pseudo steady state (PSS) was achieved. Even at maximum OLR of 2 kg COD/m 3 d, COD and biochemical oxygen demand (BOD) removals exceeded 88%. Removal of particulate fraction of organics was found to be greater than soluble fraction. Compartment-wise studies of various parameters revealed that if the OLR was larger, the number of initial compartments played significant role in the removal of organics. The values of volatile fatty acids (VFA) demonstrated that hydrolysis and acidogenesis were the main biochemical activities in the initial few compartments. Based on the tracer studies, dead space in the ABR was found to range from 23% to 34%. The flow pattern in the ABR was classified as intermediate between plug flow and perfectly mixed flows. Observations from scanning electron micrographs (SEM) also suggested that distinct phase separation takes place in an ABR. Study of organic and hydraulic shock loads revealed that ABR was capable of sustaining the type of shock loads generally experienced at a sewage treatment plant (STP).

The potential of wheat straw hydrolysate for biogas production was investigated in continuous stirred tank reactor (CSTR) and up-flow anaerobic sludge bed (UASB) reactors. The hydrolysate originated as a side stream from a pilot plant pretreating wheat straw hydrothermally (195 °C for 10–12 min) for producing 2nd generation bioethanol [Kaparaju, P., Serrano, M., Thomsen, A.B., Kongjan, P., Angelidaki, I., 2009. Bioethanol, biohydrogen and biogas production from wheat straw in a biorefinery concept. Bioresource Technology 100 (9), 2562–2568]. Results from batch assays showed that hydrolysate had a methane potential of 384 ml/g-volatile solids (VS)added. Process performance in CTSR and UASB reactors was investigated by varying hydrolysate concentration and/or organic loading rate (OLR). In CSTR, methane yields increased with increase in hydrolysate concentration and maximum yield of 297 ml/g-COD was obtained at an OLR of 1.9 g-COD/l d and 100% (v/v) hydrolysate. On the other hand, process performance and methane yields in UASB were affected by OLR and/or substrate concentration. Maximum methane yields of 267 ml/g-COD (COD removal of 72%) was obtained in UASB reactor when operated at an OLR of 2.8 g-COD/l d but with only 10% (v/v) hydrolysate. However, co-digestion of hydrolysate with pig manure (1:3 v/v ratio) improved the process performance and resulted in methane yield of 219 ml/g-COD (COD removal of 72%). Thus, anaerobic digestion of hydrolysate for biogas production was feasible in both CSTR and UASB reactor types. However, biogas process was affected by the reactor type and operating conditions.

Hydrogen (H 2 ) is one of renewable energy sources known for its non-polluting and environmentally friendly nature, as its end combustion product is water (H 2 O). The biological production of H 2 is a less energy intensive alternative where processes can be operated at ambient temperature and pressure. Dark fermentation by bacterial biomass is one of multitude of approaches to produce hydrogen which is known as the cleanest renewable energy and is thus receiving increasing attention worldwide. The present study briefly reviews the biohydrogen production process with special attention on the effects of several environmental and operational factors towards the process. Factors such as organic loading rate, hydraulic retention time, temperature, and pH studied in published reports were compared and their influences are discussed in this work. This review highlights the variations in examined operating ranges for the factors as well as their reported optimum values. Divergent values observed for the environmental/operational factors merit further exploration in this field.

The study is aimed at defining possible correlations between sludge retention time (SRT), biomass growth, biomass activity and membrane cleaning requirements in a submerged membrane bioreactor (MBR). For the experimental campaign, a lab-scale MBR was continuously fed on pre-settled municipal wastewater and operated to obtain complete nitrification. Volumetric loading rate of 1.2 gCOD L À1 d À1 was maintained by fixing the permeate flux and diluting the influent wastewater as required. Experimental runs were performed adopting SRT of 20, 40, 60 and 80 days. Results were integrated with data from a previous experiment with complete sludge retention. A significant correlation between SRT and organic loading rate has been observed. Results of the respirometric measurements suggested that the biomass activity is weakly affected by the sludge age. Membrane cleaning requirements also appear to be scarcely dependent on SRT and on the average membrane cleaning was required about every 2 months. Further investigation of the sludge physical properties indicate that the capillary suction time can be considered as a suitable early warning parameter for the cleaning schedules. The findings allow the conclusion that SRT longer than 40 days could be considered for reliable operation of MBRs for municipal wastewater treatment.

This work reviews the potential of anaerobic digestion for material recovery and energy production from fruit and vegetable wastes (FVW). These wastes contain 8-18% total solids (TS), with a total volatile solids (VS) content of 86-92%. The organic fraction includes about 75% easy biodegradable matter (sugars and hemicellulose), 9% cellulose and 5% lignin. Anaerobic digestion of FVW was studied under different operating conditions using different types of bioreactors. It permits the conversion of 70-95% of organic matter to methane, with a volumetric organic loading rate (OLR) o f 1-6.8 g versatile solids (VS)/l day. A major limitation of anaerobic digestion of FVW is a rapid acidification of these wastes decreasing the pH in the reactor, and a larger volatile fatty acids production (VFA), which stress and inhibit the activity of methanogenic bacteria. Continuous two-phase systems appear as more highly efficient technologies for anaerobic digestion of FVW. Their greatest advantage lies in the buffering of the organic loading rate taking place in the first stage, allowing a more constant feeding rate of the methanogenic second stage. Using a two-stage system involving a thermophilic liquefaction reactor and a mesophilic anaerobic filter, over 95% volatile solids were converted to methane at a volumetric loading rate of 5.65 g VS/l d. The average methane production yield was about 420 l/kg added VS.

An aerobic submerged filter (ASF) using volcanic scoria stones as packing media was evaluated. The wastewater used was a mixture of sewage with sugar to obtain organic matter concentrations between 28 and 3230 mg CODt/L, hydraulic rates up to 2.88 m 3 /m 2 d and organic loading rates between 0.45 and 9.4 kg CODt/m 3 d. The system removed 80% of CODt as average for organic loading rates between 0.45 and 3 kg CODt/m 3 d and 54% at the higher rate (9.4 kg CODt/m 3 d). It was not necessary to backwash the filters, a negligible pressure drop and a good biomass attachment in the volcanic scoria stones was observed. Nitrification and organic matter biodegradation were carried out simultaneously with a nitrate production of 90% up to 1.7 kg CODt/m 3 d. Tracer studies revealed a completed mixed hydraulic pattern which was not affected by the presence of biomass.

Manure Low temperature a b s t r a c t Biogas production in anaerobic digestion in farm-scale units is typically performed under mesophilic conditions when used for producing domestic fuel and stabilizing animal waste for the use of digested manure as a fertilizer. Previous studies on the digestion of llama and cow manure have shown the feasibility of producing biogas under altiplano conditions (low pressure and low temperature) and of llama manure as a promising feedstock. The present study concerns the utilization of various mixtures of feedstocks from the Bolivian altiplano under low temperature conditions (18-25 C). Laboratory scale experiments were performed on the digestion of mixtures of llama, sheep and cow manure in a semicontinuous process using ten 2-L stainless steel digesters to determine the effects of organic loading rate (OLR) and the feed composition. The semi-continuous operation of mixture of llama-cow-sheep manure proved to be a reliable system, which could be operated with good stability. The results suggest that in a system digesting a mixture of llama-cow-sheep manure at low temperature (18-25 C) the maximum OLR value is between 4 and 6 kg VS m 3 d À1 . The methane yields obtained in the mixture experiments were in the range 0.07-0.14 m 3 kg À1 VS added, with a methane concentration in the gas of between 47 and 55%. (G. Lidé n). A v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m h t t p : / / w w w . e l s e v i e r . c o m / l o c a t e / b i o m b i o e 0961-9534/$ -see front matter ª b i o m a s s a n d b i o e n e r g y 3 3 ( 2 0 0 9 ) 5 2 7 -5 3 3

The feasibility of using an up-flow anaerobic sludge blanket (UASB) reactor followed by activated sludge (AS system) for the treatment of wastewater discharged from dairy factory was explored. The UASB reactor was operated at a hydraulic retention time (HRT) of 24 h and organic loading rates (OLRs) ranging from 1.9 to 4.4 kgCOD/m 3 .d. The average total chemical oxygen demand (COD total ) and total biological oxygen demand (BOD 5total ) concentrations of the UASB reactor effluent were 1385 and 576 mg/l, corresponding to percentage removal of 69% and 79%, respectively. Total suspended solids (TSS) and volatile suspended solids (VSS) removal averaged above 72% and 75%, respectively. Residual phosphorous and oil and grease concentrations of the UASB reactor effluent were 8.2 and 44 mg/l, corresponding to percentage removal values of 63% and 83%, respectively. This good performance could be attributed to the relatively long sludge residence time (SRT =76 d) imposed to the reactor. Total and faecal coliform counts were reduced in the treated effluent by a value of 1.07 and 0.9 log 10 , respectively. The net sludge yield coefficient was found to be 0.2 g VSS per g COD total removed per day, corresponding to 20% of the total influent COD imposed to the UASB reactor. The volatile solids / total solids (VS/TS) ratio of 0.66 of excess sludge revealed its good quality. Preliminary batch experiments of the AS system treating UASB reactor effluent indicated first-order removal kinetics between total organic carbon (TOC) and contact time. The TOC removal reached 80%, resulting in only 47 mg/l in the final effluent at a HRT of 2.0 h. Accordingly, the AS system was operated at a HRT of 2.0 h. The system achieved a substantial reduction of COD total , BOD 5 total , TSS and oil and grease resulting effluent quality with residual values of only 35.0, 7.0, 14.0 and 2.8 mg/l, respectively. The geometric mean of total and faecal coliform counts was reduced by a value of 1.28 and 1.64 log 10 , respectively. Based on these results, it is recommended to use of an integrated system consisting of a UASB reactor followed by the AS system for the treatment of a combined dairy and domestic wastewater to produce a good effluent quality complying with the standards for discharge into agricultural drains.

AbstractÐA review concerning the characterisation, production, modelling, signi®cance and implications of soluble microbial products (SMP) in wastewater treatment is presented. The precise de®nition of SMP is open to debate, but is currently regarded as``the pool of organic compounds that are released into solution from substrate metabolism (usually with biomass growth) and biomass decay'', although for anaerobic systems volatile fatty acids are not included as SMP. Some of the SMP have been identi®ed as humic and fulvic acids, polysaccharides, proteins, nucleic acids, organic acids, amino acids, antibiotics, steroids, exocellular enzymes, siderophores, structural components of cells and products of energy metabolism. Crucially, SMP have been found to comprise the majority of soluble organic material in the euents from biological treatment processes and their presence is, therefore, of particular interest in terms of achieving discharge consent levels for BOD and COD. SMP also exhibit several characteristics, such as toxicity and metal chelating properties, which eect the performance of the treatment system, and their presence has also been shown to adversely aect the kinetic activity and the¯occulating and settling properties of sludge. This review outlines some important discoveries with regard to the MW distribution, biodegradability and treatability of SMP and also the eect of process parameters on their production. It also summarises the attempts at incorporating SMP formation into the modelling of wastewater treatment. However, it concludes that the knowledge regarding SMP is far from complete and that much work is still required to fully understand their contribution to the treatment process; some of these future research areas are then outlined. #

The treatment and reuse of domestic wastewater using an anaerobic baffled reactor (ABR) followed by a duckweed pond (DWP) were the main theme of the present study. The ABR was fed continuously with domestic wastewater at four HRTs ranging from 8 to 24 h and corresponds to organic loading rates ranging from 0.67 to 2.1 kg COD/m3/day. The ABR effluent was fed to a DWP operating at 10 and 15 days. The performance of the ABR at the four HRTs gave satisfactory results. Chemical oxygen demand (COD) removal was between 68 and 82%. Fecal coliform removal was between 1 to 2 logs. The 12- and 18-h hydraulic retention times (HRTs) gave close results, as indication of the possible selection of the 12-h HRT as the optimum operation for the ABR based on economic advantage. The ABR compartmentalized structure gave results higher than those produced by the one-stage digester and similar to those produced by the two-phase anaerobic digestion process. Duckweed ponds as post-treatment operated at 10 days and 15 days gave the best results at 15-day HRT, where it was possible to remove 73.4% of nitrogen and 65% of phosphorus and produce protein-rich dry duckweed of 105 kg/ha/day on average. The removal of fecal coliform (FC) in duckweed ponds was 3–4 logs. The final treated domestic sewage characteristics proved its compliance with the Egyptian standards for reuse in restricted irrigation.

This paper examines the effect of organic loading rate on the removal efficiency of COD and TOC anaerobic thermophilic fluidized bed reactor (AFBR) in the treatment of cutting-oil wastewater at different hydraulic retention time (HRT) conditions. The essays are development at laboratory scale using a porous support medium.

A kinetic study of the anaerobic digestion process of palm oil mill effluent (POME) was carried out in a laboratory-scale up-flow anaerobic sludge fixed film (UASFF) bioreactor at mesophilic temperature (38 8C). Influent COD concentrations in the range of 5260-34725 mg/l were applied at steady state conditions. Chen and Hashimoto kinetic equation and a simplified Monod's model was employed to describe kinetics of POME anaerobic digestion at organic loading rates in the range of 0.88-34.73 g COD/l day. The hydraulic retention times (HRT) ranged between 1 and 6 days. Throughout the experiment, the removal efficiency of COD was between 80.6 and 98.6%. The methane production rate was between 0.287 and 0.348 l CH 4 /g COD removed day. Biokinetic coefficients; apparent half-velocity constant, A, half-velocity constant, K s, maximum specific microbial growth rate, m m , methane yield constant, Y M , and growth yield constant, Y x , were evaluated. The apparent rate constants, K, calculated by simplified Monod model were in the range of 2.9-7.4 l CH 4 /g COD day. At different influent COD concentrations, K values showed a linear relationship with variations of VSS content of the reactor. #

Cereal distillers grains, a by-product from bioethanol industry, proved to be a suitable feedstock for biogas production in laboratory scale anaerobic digesters. Five continuously stirred tank reactors were run under constant conditions and monitored for biogas production and composition along with other process parameters. Iron additives for sulfide precipitation significantly improved the process stability and efficiency, whereas aerobic pretreatment of the grains had no effect. The microbial communities in the reactors were investigated for their phylogenetic composition by terminal restriction fragment length polymorphism analysis and sequencing of 16S rRNA genes. The bacterial subcommunities were highly diverse, and their composition did not show any correlation with reactor performance. The dominant phylotypes were affiliated to the Bacteroidetes. The archaeal subcommunities were less diverse and correlated with the reactor performance. The well-performing reactors operated at lower organic loading rates and amended with iron chloride were dominated by aceticlastic methanogens of the genus Methanosaeta. The well-performing reactor operated at a high organic loading rate and supplemented with iron hydroxide was dominated by Methanosarcina ssp. The reactor without iron additives was characterized by propionate and acetate accumulation and high hydrogen sulfide content and was dominated by hydrogenotrophic methanogens of the genus Methanoculleus.

The effects of SRT, OLR and feed temperature on the performance of membrane bioreactor treating high strength municipal wastewater

Ahmed H. Birima, Megat Johari Megat Mohd Noor, Thamer A. Mohammed, Azni Idris, Suleyman A. Muyibi, H. Nagaoka, J. Ahmed & L.A. Abdul Ghani

Abstract

The effects, of sludge retention time (SRT), feed temperature (T f ) and organic loading rate (OLR) on submerged membrane bioreactor (SMBR) performance were studied using hollow fibers (nominal pore size 0.4 µm) immersed in an aeration tank. A synthetic wastewater representative of high strength municipal wastewater was used in the study. Ten experimental runs were carried out using full factorial design with three factors and three levels (low, medium and high). These levels were 25, 30 and 35 days for SRT, 20, 30 and 40°C for T f and 1.73, 4.03 and 6.82 kg COD/m3 d for OLR. Variation of OLR, SRT and T f affected the biomass development significantly. The higher OLR trials resulted in higher MLVSS/MLSS ratio and also higher increasing rate of MLSS (d(MLSS)/ (dt)). For the low level OLR trials MLVSS/MLSS ratio varied between 75.3 and 82.3% and d(MLSS)/(dt) from 87.5 to 297.3 mg/l.d, whereas, for the high OLR trials they varied between 80.4 and 83.7% and 1355.4–2120.1 mg/l.d respectively. For the higher OLR, a higher aeration rate was applied to fulfill the DO demand. Therefore, for the low level OLR trials, the aeration rate and the DO were varied from 6 to 12 m3/m2 membrane area per hour and from 3.7 to 5.7 mg/l, respectively, whilst for the high OLR trials they varied from 6 to 18 m3/m2 membrane area/h and from 0.9 to 4.4 mg/l respectively. The permeate COD and NH3-N under different operating conditions varied from 0 to 32 mg/l, and from 0.004 to 0.856 mg/l, respectively. The interaction effects of SRT and T f on COD removal efficiency was found to be insignificant. Increasing OLR did not affect COD removal. The optimum removal efficiency of ammonia nitrogen for the low and high strength wastewater was obtained at operating conditions of high SRT and low T f . The pH increased significantly in the aeration tank and the increase was well correlated with the feed pH (r 2 = 0.8336 for low OLR and 0.9106 for high OLR).

Dairy wastewater was evaluated for biological hydrogen (H 2 ) production in conjugation with wastewater treatment in a suspended growth sequencing batch reactor (AnSBR) employing sequentially pretreated [heat-shock (100 • C, 2 h) and acid (pH 3.0, 24 h)] mixed consortia. The bioreactor was operated at mesophilic (room) temperature (28 ± 2 • C) under acidophilic conditions (pH 6.0) with a total cycle period of 24 h consisting of FILL (15 min), REACT (23 h), SETTLE (30 min), and DECANT (15 min) phases at three different organic loading rates (OLR) of 2.4, 3.5, and 4.7 Kg COD/m 3 -day, respectively. H 2 evolution rate differed significantly with the substrate/OLR of wastewater used as substrate [OLR 2.L ]. Substrate (COD) removal efficiency of 64.7 (substrate degradation rate (SDR): 1.577 Kg COD/m 3 -day), 60 (SDR: 3.168 Kg COD/m 3 -day), and 50% (SDR-3.2 Kg COD/m 3 -day), respectively, was observed at operating OLR of 2.4, 3.5, and 4.7 Kg COD/m 3 -day, respectively. The system showed rapid stabilization tendency (2.4 Kg COD/m 3 -day: 39 days; 3.5 Kg COD/m 3 -day: 14 days; 4.7 Kg COD/m 3 -day: 24 days) with respect to H 2 generation and COD reduction. A surge in pH values from 5.8 to 4.5 (2.4 Kg COD/m 3 -day), 5.82 to 4.62 (3.5 Kg COD/m 3 -day), and 6.28 to 4.56 (4.7 Kg COD/m 3 -day) was observed during stabilized phase of operation.

A study of anaerobic digestion of piggery wastewater was carried out in a laboratory-scale sludge bed reactor as a secondary treatment. The effect of organic volumetric loading rates (B V ) in the range of 1.0-8.1 g TCOD/l d on the process performance was evaluated. The best results were obtained at B V equal to or lower than 4 g TCOD/l d. At higher B V values, the removal efficiency of the process decreased suddenly. A linear relationship was found between the effluent SCOD and the TVFA/alkalinity ratio (P ). A relationship was found among the different operational variables (B V , removal efficiency, effluent soluble COD, soluble COD removal rate (R), retention factor (/), specific microbial growth rate (l), methane production rate per volume of reactor and per volume of waste treated--Q M and q M , respectively) and the corresponding regression equations were obtained. An increase of B V determined a decrease of removal efficiency, / and q M and an increase of effluent soluble COD, l, R and Q M . The value of the maximum specific microbial growth rate (l M ) determined through the equation that correlated B V and l was found to be 0.19 d À1 . This value was of the same magnitude as those reported in other works of anaerobic digestion of piggery waste.

The objective of this study was to investigate the performance of a pilot-scale membrane bioreactor (MBR) system for the treatment of a highly concentrated mixed wastewater from wet processes (dyeing, finishing, and sizing) of a denim producing textile industry. The MBR system, containing a submerged hollow fiber membrane module in the aeration tank, was operated aerobically for about 3 months on-site at a continuous flow mode. The system was operated at two different operation stages: (1) no sludge wastage with a typical permeate flux of 20 L/m 2 h and (2) a solids retention time of 25 days with the same flux. During the whole operation period, despite the high dissolved solids content in the influent, very high treatment efficiencies were achieved. The performance of the MBR system was not adversely affected by the variations in the influent characteristics, food/ microorganism ratio, organic loading rate, and specific substrate utilization rate. The average values of some effluent quality parameters found in the entire operation period were color, 53 Pt Co; turbidity, 0.31 NTU; TSS, 0.6 mg/L; BOD 5 , 15 mg/L; COD, 37 mg/L; NH 3 ÁN, 1.0 mg/L; NO 3 ÁN, 9.6 mg/L; and TN, 10.5 mg/L. Reduction in permeate flux due to membrane fouling was observed only once during all operation and such fouling was removed by applying chemical backwashing and chemical cleaning procedures. The results indicated that complex and highly polluted denim textile wastewaters could be treated very effectively by MBR systems. Color values from as high as 8100 Pt Co levels were significantly reduced to about 50 Pt Co levels, indicating that MBR effluent could be reused in the production processes.

An overall treatment process for the removal of nitrogen, methane production and obtention of valuable fertilizers from dairy manure has been investigated in laboratory scale. Solid and liquid fractions were separated by flocculation and screening. The solid fraction contained 81.6%, 84.4%, 58.6% and 85.2% of TS, VS, TKN-N and P T originally present in manure. Batch anaerobic digestion of this solid fraction at 50°C resulted in methane production of 29.0 L CH 4 /kg. The liquid fraction, free of suspended solids, was satisfactorily treated at 35°C in an upflow anaerobic sludge blanket reactor operating stably at an organic loading rate of 40.8 g COD/(LÁd) reaching a methane production of 10.3 L CH 4 /(LÁd). Accumulation of volatile fatty acids did not occur. Ammonia nitrogen concentration in the anaerobic effluent fluctuated between 850-1170 mg NH þ 4 -N/L and was reduced to values less than 100 mg NH þ 4 -N/L by struvite precipitation.

The possibility of shifting a methanogenic process for hydrogen production by changing the process parameters viz., organic loading rate (OLR) and hydraulic retention time (HRT) was evaluated. At first, two parallel semi-continuously fed continuously stirred tank reactors (CSTR) were operated as methanogenic reactors (M1 and M2) for 78 days. Results showed that a methane yield of 198-218 L/kg volatile solids fed (VS fed ) was obtained when fed with grass silage at an OLR of 2 kgVS/m 3 /d and HRT of 30 days. After 78 days of operation, hydrogen production was induced in M2 by increasing the OLR from 2 to 10 kgVS/m 3 /d and shortening the HRT from 30 to 6 days. The highest H 2 yield of 42 L/kgVS fed was obtained with a maximum H 2 content of 24%. The present results thus demonstrate that methanogenic process can be shifted towards hydrogen production by increasing the OLR and decreasing HRT.

A novel anaerobic hybrid reactor (AHR) configuration incorporating floating support media for biomass immobilization and biogas recirculation for enhanced mixing was used for anaerobic digestion of dairy manure. No pretreatment or solid liquid separation was applied. The reactor was operated at high influent volatile solids (VS) and organic loading rates (OLR) of up to 9.87% and 7.30 g VS/l day, respectively. After 149 days of continuous operation the results revealed that a high amount (38.1 g VSS) of biomass was able to attach itself to the support medium being used. The investigated AHR configuration achieved COD, BOD, TS, and VS removal efficiencies of 48-63, 64-78, 55-65, and 59-68%, respectively, at a hydraulic retention time (HRT) of 15 days. The corresponding average methane production value obtained in this study was 0.191 l/g VS added.

This desk study deals with the mechanisms and parameters affecting particles separation from wastewater in mainly upflow anaerobic reactors. Despite the fact that the functioning of upflow anaerobic sludge blanket (UASB) systems depends on both physical parameters and biological processes, the physical parameters have been barely reported in the literature. The reason is that the underlying mechanisms are very complex and depend on various interrelated parameters. In addition, the lack of a serious attempt to gather the entire physical theme into one picture has resulted in just a superficial understanding of this field of science. Better understanding of the interaction and role of these parameters is essential for the development of anaerobic treatment technologies. In this study, the various parameters that might affect the solid liquid separation process by filtration through the sludge bed of a UASB have been elaborated. These parameters have been classified into (1) reactor operational conditions (temperature, organic loading rate, hydraulic retention time and upflow velocity), (2) influent characteristics (influent concentration, influent particle size and influent particle charge) and (3) sludge bed characteristics (particle size distribution, extracellular polymeric substances, and charge). The overall output of this study includes (1) a literature review, (2) structuring of this field of science, and (3) highlighting fields where research is needed.

Avaliou-se o desempenho de um reator anaeróbio de manta de lodo (UASB) em escala laboratorial quanto à eficiência na remoção da carga poluidora, utilizando como substrato leite tipo B, diluído com concentração média de 2.500 mg.L -1 , similar aos efluentes de laticínios quando descartado o soro. Durante os 205 dias de operação, o reator foi avaliado em relação à eficiência, de acordo com a carga orgânica volumétrica (COV) aplicada. O incremento da COV aplicada foi realizado com a redução do tempo de detenção hidráulica; com isso, os TDH(s) médios aplicados no reator foram de 12, 20, 18 e 16 horas. A carga orgânica biológica (COB) inicial, ou seja, de partida, foi de 0,054 kgDBO.kgSVT -1 .dia -1 . O reator apresentou eficiências de 24, 43, 52 e 39%, na remoção de DQO T , e 22, 22, 17 e 17% na remoção de sólidos totais para os respectivos TDH(s) aplicados. Os melhores resultados do reator UASB na remoção de matéria orgânica foram obtidos com os TDH (s) de 20 e 18 horas. Nas condições de temperatura, carga orgânica volumétrica (COV) e tempo de detenção hidráulica (TDH) aplicados, o reator demonstrou boas condições de tamponamento, sendo desnecessária a correção do pH, o que significa minimização de custos.

Fully submerged laboratory scale hollow fiber microfiltration module was used to treat a food industry wastewater in Malaysia. Permeate extraction was carried out continuously under a suction pressure not exceeding 0.9 bar. The module is aerated from beneath the microfiltration module to provide the crossflow effect and the oxygen requirement for the biological process. Active sludge from activated sludge plant at the factory was used in the start-up with a food/microorganisms (F/M) ratio of about 0.6, which later reduced further with time to 0.13 subject to the increase in the mixed liquor suspended solids (MLSS) and the permeate extraction rate. Primary effluent with chemical oxygen demand (COD) ranged between 1500 and 3000 mg/l was used in the study. MLSS of over 5500 mg/l were reached after nearly three month of filtration run. Permeate COD and turbidity reduction of over 97% and 99% respectively, were achieved. Dark streaks that formed on the inner side of the membrane surface are responsible for the declining permeate turbidity in the second month of operation since the membrane nominal size remains relatively unchanged.

In the present study, thermophilic anaerobic digestion of wheat straw stillage was investigated. Methane potential of stillage was determined in batch experiments at two different substrate concentrations. Results showed that higher methane yields of 324 ml/g-(volatile solids) VS added were obtained at stillage concentrations of 12.8 g-VS/L than at 25.6 g-VS/l. Continuous anaerobic digestion of stillage was performed in an up-flow anaerobic sludge blanket (UASB) reactor at 55°C with 2 days hydraulic retention time. Results showed that both substrate concentration and organic loading rate (OLR) influenced process performance and methane yields. Maximum methane yield of 155 ml CH 4 /g-COD was obtained at stillage mixtures with water of 25% (v/v) in the feed and at an OLR of 17.1 g-COD/(l.d). Soluble chemical oxygen demand (SCOD) removal at this OLR was 76% (w/w). Increase in OLR to 41.2 g-COD/(l.d) and/or stillage concentration in the feed to 33-50% (v/v) resulted in low methane yields or complete process failure. The results showed that thermophilic anaerobic digestion of wheat straw stillage alone for methane production is feasible in UASB reactor at an OLR of 17.1 g-COD/(l.d) and at substrate concentration of 25% in the feed. The produced methane could improve the process energy and economics of a bioethanol plant and also enable to utilize the stillage in a sustainable manner.