Start Up Performance Of A Mesophilic Anaerobic Digester Without External Inoculums (original) (raw)
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Startup of Anaerobic Mesophilic Digesters
Proceedings of the Water Environment Federation, 2006
Many operators have started up mesophilic digesters, but everyone has differing stories and experiences. This paper is a combination of the startup of several mesophilic anaerobic digesters, with very low seeding to fully seeded conditions. Upper Occoquan Sewage Authority (UOSA) operates the Millard H. Robbins Water Reclamation Plant. UOSA started three anaerobic digesters between August 2000 and March 2001 as part of a major expansion which brought the permitted capacity of the facility from 32 to 54 million gallons per day (mgd). Alexandria Sanitation Authority (ASA) operates the ASA Advanced Wastewater Treatment Plant with an average plant influent flow of 54 mgd. ASA started four anaerobic digesters between May and October 2005 as part of a solids upgrade that added pre-pasteurization and two new anaerobic digesters. This paper will provide a useful roadmap for digester startups for all operators.
Two years of operational data of the pilot anaerobic digester system was used. 2-Stage digestion for food waste treatment was stable during highly variable loading. Methane yield from 2-stage operation was higher than for single stage digestion. a b s t r a c t Single and two-phase operations were compared at mesophilic operating conditions using a digester system consisting of three 5-m 3 reactors treating food waste generated daily within the university campus kitchens. When normalizing the methane production to the daily feedstock characteristics, significantly greater methane was produced during two-phase mesophilic digestion compared to the single-stage operation (methane yield of 380 vs 446-L CH 4 kg VS À1 ; 359 vs 481-L CH 4 kg COD À1 removed for single vs two stage operation). The fermentation reactor could be maintained reliably even under very low loading rates (0.79 ± 0.16 kg COD m À3 d À1) maintaining a steady state pH of 5.2.
Fermentation
The start-up of two-stage, semi-continuous mesophilic anaerobic digestion (TSAD) of food waste is stabilized by altering the hydraulic retention time (HRT) and organic-loading rate (OLR). The volumetric biogas yield and composition are studied at OLR (0.25–0.50 gVS/L/d) and HRT (10, 20, 40 days) initiating at OLR 0.25 g VS/L/d and HRT of 20 and 40 days for the respective reactors. Methane (CH4) from the first stage of the two-staged reactor decreased from 18.20% to 0.06%, fostering hydrogen production in 44 days when the HRT was reduced from 20 to 10 days and OLR increased from 0.25 gVS/L/d to 0.50 gVS/L/d. During the alarming volatile fatty acids (VFA)/alkalinity ratio of 0.76, feeding to the second-stage reactor was halted until pH was restored to 7.00. The restoration of methanogens was evident by an increase in methane from 39.15% to 67.48%. A stable TSAD system produced 22.32 ± 4.16 NmL/gVS and 161.02 ± 17.72 NmL/gVS of yield in respective reactors. Thus, TSAD paves the path fo...
Design considerations and operational performance of anaerobic digester: A review
Cogent Engineering, 2016
Due to the decline in fossil fuel reservoirs, the researchers emphasized more on the production of biogas from organic waste. Producing the renewable energy from biodegradable waste helps to overcome the energy crisis and solid waste management, which is done by anaerobic digestion. Anaerobic digestion is the controlled breakdown of organic matter into methane gas (60%), carbon dioxide (40%), trace components along with digested used as soil conditioner. However, there is vast dearth of literature regarding the design considerations. The batch digestion system yields a cost-effective and economically viable means for conversion of the food waste to useful energy. It is therefore recommended that such process can be increasingly employed in order to get and simultaneously protect the environment. This paper aims to draw key analysis and concern about the design considerations, analysis of gas production, substrates and inoculua utilization, uses and impacts of biogas.
Simple approaches to start-up anaerobic digestion systems for biogas production
2012
The start-up of anaerobic digestion processes is a complex problem, which determines the entire evolution of the system. In spite of its importance, this issue has not received so far a significant attention. This paper presents two simple startup strategies for an anaerobic digestion process, which have been developed based on the system dynamics. Both strategies consists of switching the dilution rate between minimum and maximum levels and then to an optimal level to drive the system towards a steady state characterized by maximum production of biogas. The main difference between the two policies consists in the type of measurement assumed: while for the first strategy it is supposed that the entire state of the system is available, for the second approach only the outflow rate of biogas is needed. Simulation results are presented to illustrate the principle of the two approaches.
An analytical model to study the performance of an anaerobic digester
Agricultural Wastes, 1983
This paper is concerned with the mass balance equations describing an anaerobic digester working essentially for the production of biogas together with the reduction of the polluting organic content of agricultural and industrial discharges. The model of the digester is built up starting from the fundamental equations for hydrolysis, acidogenesis and methanogenesis. The steadystate equilibrium situation is then fully investigated and sample calculations are perJormed and discussed. An improvement of the model is finally presented and its implications are investigated. The work shouM represent a step towards establishing a design tool for the engineer undertaking the task of defining the characteristics of a fullscale digester, NOMENCLATURE a Maximum hydrolysis rate (mg litre-1 s-1). A w Yield coefficient for methane formers (dimensionless, milligrams of substrate per milligram of bacteria). A. Yield coefficient for acid formers (dimensionless, milligrams of substrate per milligram of bacteria). B w Specific consumption rate for the methane-forming bacteria substrate (s-1). B z Specific consumption rate for the acid-forming bacteria substrate (s-1).
Bioresource Technology, 2008
The aim of this paper was to analyze the biomethanization process of food waste (FW) from a university campus restaurant in six reactors with three different total solid percentages (20%, 25% and 30% TS) and two different inoculum percentages (20-30% of mesophilic sludge). The experimental procedure was programmed to select the initial performance parameters (total solid and inoculum contents) in a lab-reactor with V: 1100 mL and, later, to validate the optimal parameters in a lab-scale batch reactor with V: 5000 mL. The best performance for food waste biodegradation and methane generation was the reactor with 20% of total solid and 30% of inoculum: give rise to an acclimation stage with acidogenic/acetogenic activity between 20 and 60 days and methane yield of 0.49 L CH4/g VS. Also, lab-scale batch reactor (V: 5000 mL) exhibit the classical waste decomposition pattern and the process was completed with high values of methane yield (0.22 L CH 4 /g VS). Finally, a protocol was proposed to enhance the start-up phase for dry thermophilic anaerobic digestion of food waste.
Revista Brasileira de Engenharia de Biossistemas, 2008
The objective of this work was the implantation and evaluation of three sludge anaerobic digestionsystems. The system A configuration was defined by five continuous flow sequential anaerobicreactors (SAR) with effluent recycling. System B had the same layout, but recirculation wassubstituted by mechanical mixers installed in each reactor. System C was composed by only onecontinuous flow stirred tank reactor. The systems were evaluated by weekly monitoring of physical-chemical parameters. Samples were taken from influent, effluent and intermediary ports during anoperation period of 115 days. During the most stable operational period (PHASE II), the resultsindicated total solids removal rate of 95, 40 and 29%, and volatile solids removal rate of 95, 34 and22%, for System A, B and C, respectively. The sequential anaerobic reactors (System A and B)presented better performance than conventional digestor (System C).