Anaerobic digestion and in situ electrohydrolysis of dairy bio-sludge

A novel treatment method based on anaerobic digestion and in-situ electrohydrolysis of dairy bio-sludge was investigated in this article. The electrohydrolysis was carried out inside the anaerobic reactor using graphite anode and stainless steel cathode. The electrons released by the graphite anode combines with the proton released due to electrohydrolysis of fatty acids which resulted in the formation of hydrogen gas. The experiments were conducted using a DC power source under continuous and intermittent mode of input voltage ranging from 0.5 to 2.5 V for varying influent volatile solids concentration at a pH 5.3 ± 0.2. The results favored intermittent mode of input voltage rather than continuous supply. For an influent total solid concentration of 7% (64,120 mg/L VS), intermittent input voltage of 2 V, and a hydraulic retention time of 15 days resulted in a volatile solids and soluble COD removal efficiency of 83 and 74%, while the cumulative gas generation was 1,051 L with a hydrogen content of 72%.     

Controlled shear affinity filtration (CSAF): a new technology for integration of cell separation and protein isolation from mammalian cell cultures

Up-flow anaerobic sludge blanket (UASB) reactors are being used with increasing regularity all over the world, especially in India, for a variety of wastewater treatment operations. Consequently, there is a need to develop methodologies enabling one to determine UASB reactor performance, not only for designing more efficient UASB reactors but also for predicting the performance of existing reactors under various conditions of influent wastewater flows and characteristics. This work explores the feasibility of application of an artificial neural network-based model for simulating the performance of an existing UASB reactor. Accordingly, a neural network model was designed and trained to predict the steady-state performance of a UASB reactor treating high-strength (unrefined sugar based) wastewater. The model inputs were organic loading rate, hydraulic retention time, and influent bicarbonate alkalinity. The output variables were one or more of the following, effluent substrate concentration (Se), reactor bicarbonate alkalinity, reactor pH, reactor volatile fatty acid concentration, average gas production rate, and percent methane content of the gas. Training of the neural network model was achieved using a large amount of experimentally obtained reactor performance data from the reactor mentioned above as the training set. Training was followed by validation using independent sets of performance data obtained from the same UASB reactor. Subsequently, simulations were performed using the validated neural network model to determine the impact of changes in parameters like influent chemical oxygen demand (COD) concentration and hydraulic retention time on the reactor performance. Simulation results thus obtained were carefully analyzed based on qualitative understanding of UASB process and were found to provide important insights into key variables that were responsible for influencing the working of the UASB reactor under varying input conditions.     

The application of constant recycle solids concentration in activated sludge process.

The applicability of the model derived by Ramanathan and Gaudy (Biotechnol. Bioeng., 11, 207, (1969)) for completely mixed activated sludge treatment holding the recycle solids concentration as a system constant was investigated using an actual industrial organic wastewater. Short-term experiments were conducted at various dilution rates (1/8, 1/6, 1/4, 1/2, 1/1.5 hr-1) for two recycle solids concentration values (5000 and 7000 mg/liter). The influent substrate concentration was maintained at 1000 mg/liter COD and the hydraulic recycle ratio- alpha, was kept at 0.3. It was found that for bottling plant (Pepsi Cola) wastewaters, a steady state with respect to reactor biological solids and effluent COD, at different dilution rates, could be attained, lending experimental evidence to the assumption that a steady state could be reached in developing the model and also affecting the applicability of the model in industrial organic wastewater. The reactor biological solids and effluent COD calculated from the model closely agreed with the observed values at dilution rates lower than 0.5 hr-1. Operation at dilution rates higher than 0.5 hr-1 will washout the biological solids from the reactor and the recycle substrate concentration will be apparent if the concentration of XR were not increased.     

Aerobic treatment of dairy wastewater with sequencing batch reactor systems

Performances of single-stage and two-stage sequencing batch reactor (SBR) systems were investigated for treating dairy wastewater. A single-stage SBR system was tested with 10,000 mg/l chemical oxygen demand (COD) influent at three hydraulic retention times (HRTs) of 1, 2, and 3 days and 20,000 mg/l COD influent at four HRTs of 1, 2, 3, and 4 days. A 1-day HRT was found sufficient for treating 10,000-mg/l COD wastewater, with the removal efficiency of 80.2% COD, 63.4% total solids, 66.2% volatile solids, 75% total Kjeldahl nitrogen, and 38.3% total nitrogen from the liquid effluent. Two-day HRT was believed sufficient for treating 20,000-mg/l COD dairy wastewater if complete ammonia oxidation is not desired. However, 4-day HRT needs to be used for achieving complete ammonia oxidation. A two-stage system consisting of an SBR and a complete-mix biofilm reactor was capable of achieving complete ammonia oxidation and comparable carbon, solids, and nitrogen removal while using at least 1/3 less HRT as compared to the single SBR system.     

Bioaugmentation and treatment of cephalexin drug-based pharmaceutical effluent in an upflow anaerobic fluidized bed system

Cephalexin is a constituent of the cephalosporin group used for the treatment of bronchitis and other heart diseases due to its enhanced oral activity. The effluent from these industries contains a disintegrated form of the drug contributing high chemical oxygen demand (COD), volatile solids and organic solvent. A laboratory-scale study was conducted to evaluate the efficiency of a fluidized bed reactor operated under anaerobic condition with bioaugmentation to treat the cephalexin containing pharmaceutical factory effluent. The main objective of the study was to show that bioaugmentation could be used to promote biological treatment to applications where conventional operation might be difficult or unfavourable. The effluent, with COD of 12,000-15,000 mg/l, was diluted and studied in single and multiple inoculation experiments with hydraulic retention times of 3-12 h. The removal efficiency after inoculation from an anaerobic sequencing batch reactor was related to influent concentration, mass of inoculum and hydraulic retention time characterized by calculating the initial food to microorganism ratio. Continuous COD removal efficiency attained a maximum value of 88.5% using bioaugmentation through periodic addition of acclimated cells every 2 days with 30-73.2 g of cells from an off-line enricher-reactor.     

Anaerobic digestion of cheese whey using up-flow anaerobic sludge blanket reactor

Anaerobic treatment of cheese whey using a 17·5-litre up-flow anaerobic sludge blanket reactor was investigated in the laboratory. The reactor was studied over a range of influent concentration from 4·5 to 38·1 g chemical oxygen demand per litre at a constant hydraulic retention time of 5 days. The reactor start-up and the sludge acclimatization were discussed. The reactor performance in terms of methane production, volatile fatty acids conversion, sludge net growth and chemical oxygen demand reduction were also presented in this paper. Over 97% chemical oxygen demand reduction was achieved in this experiment. At the influent concentration of 38·1 g chemical oxygen demand per litre, an instability of the reactor was observed. The results indicated that the up-flow anaerobic sludge blanket reactor process could treat cheese whey effectively.     

Biodegradation of acetonitrile by adapted biofilm in a membrane-aerated biofilm reactor

A membrane-aerated biofilm reactor (MABR) was developed to degrade acetonitrile (ACN) in aqueous solutions. The reactor was seeded with an adapted activated sludge consortium as the inoculum and operated under step increases in ACN loading rate through increasing ACN concentrations in the influent. Initially, the MABR started at a moderate selection pressure, with a hydraulic retention time of 16 h, a recirculation rate of 8 cm/s and a starting ACN concentration of 250 mg/l to boost the growth of the biofilm mass on the membrane and to avoid its loss by hydraulic washout. The step increase in the influent ACN concentration was implemented once ACN concentration in the effluent showed almost complete removal in each stage. The specific ACN degradation rate achieved the highest at the loading rate of 101.1 mg ACN/g-VSS h (VSS, volatile suspended solids) and then declined with the further increases in the influent ACN concentration, attributed to the substrate inhibition effect. The adapted membrane-aerated biofilm was capable of completely removing ACN at the removal capacity of up to 21.1 g ACN/m² day, and generated negligible amount of suspended sludge in the effluent. Batch incubation experiments also demonstrated that the ACN-degrading biofilm can degrade other organonitriles, such as acrylonitrile and benzonitrile as well. Denaturing gradient gel electrophoresis studies showed that the ACN-degrading biofilms contained a stable microbial population with a low diversity of sequence of community 16S rRNA gene fragments. Specific oxygen utilization rates were found to increase with the increases in the biofilm thickness, suggesting that the biofilm formation process can enhance the metabolic degradation efficiency towards ACN in the MABR. The study contributes to a better understanding in microbial adaptation in a MABR for biodegradation of ACN. It also highlights the potential benefits in using MABRs for biodegradation of organonitrile contaminants in industrial wastewater.     

Se(VI) reduction by continuous-flow reactors packed with Shigella fergusonii strain TB42616 immobilized by Ca2+-alginate gel beads

Selenium at high levels may cause adverse health effects on human beings and endanger aquatic lives due to its toxicity. Se(VI) reduction in continuous-flow reactors packed with Shigella fergusonii strain TB42616 immobilized by Ca²⁺-alginate gel beads was investigated under various hydraulic retention times (HRT) and influent Se(VI) concentrations. Removal efficiency up to 98.8 % was achieved after 96 days operation under an HRT of 5 days and an influent Se(VI) concentration of 400 mg/L. The results showed that the overall selenium removal efficiency was affected by the HRT and the bed height of the reactor but not the influent Se(VI) concentration. The steady-state data were analyzed using a mathematical model and Monod-type kinetics. Biokinetic parameters of half-velocity constants and maximum specific reduction rates were optimized using steady-state data obtained under a range of HRTs (0.73–5.0 days) at a constant influent Se(VI) concentration of 50 mg/L. The model was validated using steady-state data obtained under influent Se(VI) concentrations ranging from 10 to 400 mg/L while maintaining the HRT at 5.0 days. The high correlation coefficients between model calculated Se(VI) and Se(IV) concentrations and the experimental data indicate that the model is robust to predict the performance of the continuous-flow bioreactor.     

Anaerobic treatment of low-strength municipal wastewater by a two-stage pilot plant under psychrophilic conditions

A two-stage anaerobic treatment pilot plant was tested for the treatment of raw domestic wastewater under temperatures ranging from 21 to 14 degrees C. The plant consisted of a hydrolytic upflow sludge bed (HUSB) digester (25.5m3) followed by an upflow anaerobic sludge blanket (UASB) digester (20.36m3). The hydraulic retention time (HRT) varied from 5.7 to 2.8h for the first stage (HUSB digester) and from 13.9 to 6.5h for the second stage (UASB digester). Total suspended solids (TSS), total chemical oxygen demand (TCOD), and biochemical oxygen demand (BOD) removals ranged from 76% to 89%, from 49% to 65%, and from 50% to 77%, respectively, for the overall system. The percentage of influent COD converted to methane was 36.1%, the hydrolysis of influent volatile suspended solids (VSS) reached 59.7% and excess biomass was 21.6% of the incoming VSS. Plant performance was influenced by the wastewater concentration and temperature, yet better results were obtained for influent COD higher than 250mg/l.     

Performances of a full-scale novel multiplate anaerobic reactor treating cheese whey effluent

A 450-m(3) multiplate anaerobic reactor (MPAR) has been started-up in April 1992 for treating wastewater (whey permeate and domestic wastewater) at the Nutrinor (Lactel) cheese factory in Chambord (Québec, Canada). The MPAR consists of four superimposed sections. The liquid flows upwards from one section to the next, while the gas is collected below each plate and evacuated through side-outlets. The wastewater is concurrently distributed at the bottom of the first, second, and third sections, as 50%, 33%, and 17% of the total influent stream, respectively. Granular anaerobic sludge at an initial concentration of 30 kg of volatile suspended solids (VSS) per cubic meter of reactor liquid volume was used to inoculate the reactor. Under normal operation of the factory, the chemical oxygen demand (COD) concentration of the influent ranged from 20 to 37 kg COD m(-3). The reactor organic loading rate (OLR) fluctuated between 9 and 14.7 kg COD m(-3) d(-1) for hydraulic retention times (HRT) maintained between 55 and 68 h. At the highest OLR, the MPAR showed an efficiency of 98% and 92% for soluble and total COD removal, respectively, and a methane production rate averaging around 4 m(3) m(-3) d(-1).Biomass-specific activities ranged between 7 and 51, 1.3 and 8.5, 5.3 and 12.2, 60 and 119, and 119 and 211 mmol g(-1) VSS d(-1) for glucose, propionate, acetate, formate, and hydrogen, respectively. Average equivalent-diameter of the granules was around 0.65 mm. The MPAR reactor generally showed a large capacity for solid retention with a biomass content between 32 and 37 kg VSS m(-3). (c) 1995 John Wiley & Sons, Inc.     

Hydrodynamic performance of pilot-scale duckweed,algal-based,rock filter and attached-growth media reactors used for waste stabilisation pond research

The specific nature of fluid dynamics within waste stabilisation ponds can have a determining influence on their functional treatment performance. This paper presents the results of hydraulic tracer experiments undertaken to characterise the hydrodynamic behaviour of several pilot-scale advanced pond treatment systems (a duckweed-based pond, a conventional algal-based ‘open’ pond, a rock filter and a novel horizontal-flow attached-growth media reactor) investigated for their effectiveness at polishing a full-scale tertiary pond effluent. Duplicate tracer studies were undertaken for each of the four experimental reactors with the aid of the fluorescent dye rhodamine WT. Results from tracer studies showed flow distribution in all reactors to be highly dispersed with varying degrees of dead space volume and short-circuiting in all pilot reactors, indicating that a percentage of the total reactor volume across all treatment systems was inactive. Results from a number of calculated parameters of hydraulic performance showed that hydrodynamic efficiency was greatest in the novel horizontal-flow attached-growth media system, where a possible baffling of inflowing wastewater was thought to have promoted improved hydraulic operation. Outcomes from this research in general highlight the importance of undertaking detailed characterisations of the hydrodynamic operation of experimental pond systems and also emphasise the value of pre-validating the hydraulic design of experimental reactors used for stabilisation pond research.     

Kinetics of a fluidized-bed reactor for ground-water denitrification

A fluidized-bed reactor, with sand as the carrier and ethanol as the carbon and electron source, was investigated for the biological denitrification of ground water. The paper concentrates on the reactor's kinetics, with special emphasis on nitrite as the intermediate product. Intrinsic zero-order kinetic parameters for both nitrate and nitrite were determined by batch and continuous experiments. Values for the maximum specific nitrate and nitrite removal rates of 11 g and 6 g NO _inf3 ^sup– (g volatile suspended solids)^–1 day^–1, respectively, were obtained. These values were used to interpret nitrate and nitrate concentration profiles in an experimental fluidized-bed reactor operating at different conditions of hydraulic loading and retention time.     

The removal of nitrogen and organics in vertical flow wetland reactors: predictive models

Three kinetic models, for predicting the removal of nitrogen and organics in vertical flow wetlands, have been developed and evaluated. These models were established by combining first-order, Monod and multiple Monod kinetics with continuous stirred-tank reactor (CSTR) flow pattern. Critical evaluations of these models using three statistical parameters, coefficient of determination, relative root mean square error and model efficiency, indicated that when the Monod/multiple Monod kinetics was combined with CSTR flow pattern it allowed close match between theoretical prediction and experiment data of nitrogen and organics removal. The kinetic coefficients (derived from Monod/multiple Monod kinetics) was found to increase with pollutant loading, indicating that the coefficients may vary based on different factors, such as influent pollutant concentration, hydraulic loading, and water depth. Overall, this study demonstrated the validity of combining Monod and multiple Monod kinetics with CSTR flow pattern for the modelling and design of vertical flow wetland systems.     

Effects of quantitative shock loadings on the constant recycle sludge concentration activated-sludge process

The reliability of the process of Ramanathan and Gaudy (Biotechnol Bioeng., 13 , 125 (1971)) for the completely mixed activated-sludge process holding the recycle cell concentration, X_R, as a system constant with respect to step changes in hydraulic retention time was investigated. The experiments were run at initial dilution rates of ?, ?, ¼, and ½ hr^?1 treating a soft drink bottling wastewater. The influent substrate concentration was maintained at 1000 mg/liter chemical oxygen demand and the hydraulic recycle ratio at 0.3. The recycle sludge concentration was maintained at about 7000 mg/liter. It was found that the system could accommodate hydraulic shock loads up to 200% positive changes and down to 50%negative changes without disruption of the effluent quality. Shorter retention time of the range studied, from 2 to 8 hr, has the advantage of shorter response time with respect to the response of the concentration of biological solids in the reactor.     

Statistical modeling and optimization of biomass granulation and COD removal in UASB reactors treating low strength wastewaters

The aim of this work was to study the influence of influent chemical oxygen demand (COD), upflow velocity of wastewater, and cationic polymer additives in inoculum, on biomass granulation and COD removal efficiency in upflow anaerobic sludge blanket (UASB) reactor for treating low strength wastewater. Statistical models were formulated based on these three variables to optimize the biomass granulation and COD removal efficiency in UASB reactors using a two-level, full factorial design. For the thick inoculum used in this study, having suspended solids (SS) >80 g/l and volatile suspended solids (VSS) to SS ratio <0.3, cationic polymer additives in the inoculum showed adverse effect on biomass granulation and COD removal efficiency. It is concluded that for such thick inoculum, granulation can be obtained while treating low strength wastewaters in UASB reactor by selecting proper combination of influent COD and liquid upflow velocity so as to represent the organic loading rate (OLR) greater than 1.0 kg COD/m(3) d. Validation of model predictions for treatment of synthetic wastewater and actual sewage reveals the efficacy of these models for enhancing granulation and COD removal efficiency.     

Feeding approaches for biogas production from animal wastes and industrial effluents

Different feeding approaches were applied to a 5 l anaerobic digester in order to improve the biogas production. During operation, the reactor was fed with a mixture (9.7% w/v total solids (TS) and 7.6% w/v volatile solids (VS) in average) of pig manure with fish oil waste and waste from bentonite of edible oil filtration process, at different intervals of 24, 12 and 4 h at 15 days of hydraulic retention time. Production and quality of the biogas were practically constant at 183.7 ml (average) of biogas per gram of volatile solids available in the reactor per day, and the best biogas composition was 73.6% v/v CH₄ and 26.4% v/v CO₂.     

Anaerobic Digestion of Dairy Manure in a Hybrid Reactor with Biogas Recirculation

Summary 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.     

Anaerobic treatment of winery wastewater using laboratory-scale multi- and single-fed filters at ambient temperatures

A lab-scale investigation was conducted to examine the effectiveness of a multi-fed upflow anaerobic filter process for the methane production from a rice winery effluent at ambient temperatures. The experiment was carried in two identical 3.0-l upflow filters, a single-fed reactor and a multi-fed reactor. The results showed that the multi-fed reactor, operated at the ambient temperatures of 19–27 °C and influent chemical oxygen demand (COD) of 8.34–25.76 g/l, could remove over 82% of COD even at an organic loading rate (OLR) of 37.68 g-COD/l d and a short hydraulic retention time (HRT) of 8 h. This reactor produced biogas with a methane yield of 0.30–0.35 l-CH₄/g-COD_removed. The multi-fed upflow anaerobic filter was proved to be more efficient than the single-fed reactor in terms of COD removal efficiency and stability against hydraulic loading shocks. A linear-regression model with influent COD concentration and HRT terms adequately described the multi-fed upflow anaerobic filter system for the treatment of rice winery wastewater at ambient temperatures.     

Performance of a glucose fed periodic anaerobic baffled reactor under increasing organic loading conditions: 2. Model prediction

A model was developed for the anaerobic digestion of a glucose-based medium in an innovative high-rate reactor, the periodic anaerobic baffled reactor (PABR). The model considers each PABR compartment as two variable volume interacting sections, of constant total volume, one with high solids and one with low solids concentration, with the gas and liquid flows influencing the material flows between the two sections. For the simulation of glucose degradation, the biomass was divided into acidogenic, acetogenic and methanogenic groups of microorganisms. The kinetic part of the model accounted for possible inhibition of acidogenesis, acetogenesis and methanogenesis by volatile fatty acids. The model succeeded in predicting the reactor performance upon step increases in the organic loading rate.