Dynamic modelling and simulation of pilot scale anaerobic digestion plant treating source separated food waste and effect of recycling sludge

This study investigates the effect of recycling sludge and stability of pilot scale anaerobic digestion plant treating organic fraction of source separated food waste. Pilot plant comprises of pre-treatment, anaerobic digestion and post treatment. Anaerobic digestion is carried out under mesophilic conditions. At flow rate of 0.221 m3/d, slurry of food waste is introduced semicontinuously every day within 2 hr time span. Anaerobic digestion model No.1 (ADM1) was applied for modelling and simulation of continuous stirred tank anaerobic reactor including recycling and was implemented in AQUASIM 2.1f. Input food waste was characterized and parameters were determined as dictated by ADM1. Process parameters were obtained from pilot plant and kinetic parameters are standard parameters given in ADM1. Input Organic Loading Rate(OLR) to reactor is 4.81 kgCOD/m3.d and Hydraulic Retention Time (HRT) was 20 days. Pilot scale AD plant was simulated for 40 days. It was found that biogas production rate and gas composition vary according the intermittent feeding pattern and reactor head space contains average compositions of CH4 and CO2 of 56% and 30% (v/v) respectively. Average biogas production rate under this conditionwas 16.4 m3/d. Recycling of sludge in terms of biomass was implemented in model as an advective link. When model was simulated at 40 day solid retention time (SRT), average biogas production rate increased by 31%. By varying OLRs to reactor, stability was investigated. When input OLR was doubled in terms of hydraulic load, anaerobic reactor became unstable producing H2 (38% v/v) and CO2 (40%v/v) in reactor head space. Under this condition, bulk liquid phase pH was 4.78. Instability is further confirmed by accumulation of volatile fatty acids and inhibition of strict methanogens. ADM1 can be applied to model and simulate pilot scale anaerobic digestion plant and to screen different options before scaling up into large scale plants. 2016 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the organizing committee of 5IconSWM 2015

Optimization of adsorption-coagulation process for treatment of palm oil mill effluent (POME) using alternative coagulant

Activated carbon has been using as an adsorbent for wastewater treatment for decades. It has also been reported that use of fly ash to adsorb impurities in waste water treatment .The main objective of this study is to optimize hybrid adsorption-coagulation method for removal of color and other impurities presence in palm oil mill effluent (POME).Mango pit is a natural environmental friendly coagulant and have many advantages over commercially available aluminum and ferric salts used for water and wastewater treatment. On the other hand fly ash can be distinguished from other adsorbent in the way it desorbed and re used for the same purpose. This study further investigates the combination of fly ash with mango pit as coagulant agent for removal of color and other effluent quality parameters as TSS, TDS, COD and BOD. Palm oil mill wastewater after aeration process was collected and characterized in order to determine input conditions. Two sets of experiments were performed using jar test method namely; only adsorption using fly ash and the second is using fly ash in combination with mango pit in hybrid adsorption-coagulation system. In the first set of experiments only adsorption process studied using fly ash as an adsorbent by varying parameters affecting the process. Samples of 300ml wastewater were used with variable fly ash particle size ranging from 355pm and 500pm and operated at 200rpm. Results showed that with decrease in particle size the amount of pollutant adsorbed increased and the amount of BOD5, color, TDS, COD and TSS adsorbed increased as the weight of the boiler fly ash used was increased, therefore process was optimized using 355 pm granule size and 90g of dose which gave results in color reduction up to 91%, COD 82%, BOD5 83%, TDS 74%, TSS 78% and turbidity 93% respectively. Further in the second set of experiments equal amount of wastewater samples were investigated using hybrid adsorption-coagulation method by varying concentration of adsorbent-coagulant as (50g-0.6ml, 70g-0.8ml, 90g-1.2ml). Finally both results obtained from first and second sets of experiments were compared at optimum point, an improved trend was recorded when hybrid system was applied towards the reduction in Color from 91% to 97%, COD from 82% to 89%, BOD from 83% to 94%, TDS from 84% to 93% and TSS from 88% to 96% respectively. Hybrid coagulation-Adsorption method has not only positive impact on reduction of water quality parameters but also very cost effective and environmental friendly process. Both ingredients used in this process be obtained easily; other advantages include low sludge production and the less amount of coagulants used

Optimization of dairy waste water treatment process using combined experimental and mathematical modelling approach

In this study, combined experimental and mathematical modelling approach is developed to optimize diary waste water treatment plant. Anaerobic digestion model no.l (ADM1) was built in a simulator called Aquasim 2.1f. UASB model comprises of three CSTR (continuous stirred tank reactor) compartmenis as sludge bed, blanket and settler. Experiments were conducted at waste water treatment plant (WWTP) under three volumetric flow rates i.e. 10 m3/d, 15 m3/d and 25 m3/d. Plant is being operated at 25 m3/d. Three parameters such as cumulative biogas volume, pH and COD were measured. At the operating volumetric flow rate, WWTP was simulated with the new model and parameters such as VFA, gas composition, inhibition and biomass growth rates were obtained. By varying recycle ratio from sludge bed to blanket and settler to blanket, appropriate recycle ratio was obtained to get best fitted model, (bed to blanket - 0.8 and settler to blanket 0.6). Optimization was performed under two scenarios .i.e. by varying volumetric flow rates and input COD level. It was found that above 30 m3/d UASB become unstable producing 21% of CH4 and 75% of CO2. Also it was found that 7500 mgCOD/1 can be treated at the volumetric rate of 30 m3/d without any instability to existing WWTP

Development of new kinetic model for meshophilic biohydrogen production in Trickle bed reactor using clostrodium butyricum CWBI 1009

The aim of present study is to develop a new kinetic model for bio hydrogen production in biofilm by Clostridium butyricum CWBI1009 grown in Trickle Bed reactor running on sequence batch mode. Bio hydrogen production experiments had already been conducted using Trickle Bed Sequence Batch Reactor (TBSBR) using Clostridium butyricum CWBI1009. Measured parameters were hydrogen composition, hydrogen production rate and soluble metabolites. Controlled parameters were pH, recirculation flow rale and temperature. This reactor was operated for 62 days. Modified Anaerobic Digestion Model No.J. /(ADM1) is used to model initial phase of TBSBR. The reactor configuration, input substrate and synthetic medium were set as dictated by original ADM1. Tvvo sets of parameters were investigated in this study. In the first phase, parameters given by ADM1 were applied. In the second phase, parameters were adjusted in the range given by ADM1 until measured output and model output are in close agreement. Following parameter estimation, pH value was in close agreement with reactor operational pH value, gas flow rates and hydrogen percentage follows same Hj|;em as experimental values within 1-2% variation. However, modelled concentrations of volatile tatty acids were not well fitted with experimental data

Investigation on Sulphide inhibition of anaerobic digestion for Sulphate rich wastewater

Skim latex processing wastew iter is enriched with both organic materials and sulfates the environment as it is a nontoxic, non-volatile -Abstract: (SCV2). Sulfate does not cause any direct impact on and chemically inert compound. But biologinil transformation of sulfate under anaerobic conditions produces toxic sulfide, which inhibitory to ethanogenic microorganisms. Toxic, odorous and corrosive free hydrogen sulfide causes reduction in methane yield, significant reduction in overall treatment efficiency or complete failures in anaerobic process. According to the case study conducted, anaerobic reactor of skim latex processing wastewater treatment facility is evaluated.Its daily - wastewater generation is 100m3/day and the average COD and the BOD levels are 5,000 mg/1 and •1000 mg/1 respectively. The COD/SOp2 of the feedstock is 6.25. Although the expected efficiency of the reactor is 50%-80%, the actual COD removal efficiency is only 42% due to sulphide inhibition. Therefore, conventional anaerobic treatment cannot be applicable to skim latex wastewater without taking sufficient precautions to minimize sulfiti 2 inhibition and hydrogen sulfide emission. Microaeration is proposed as an option for treatment c: sulphate rich wastewater

Investigation of stability of anaerobic digestion of food waste in a plug flow reactor using mathematical modeling and simulation

Anaerobic treatment has gained wide acceptance as a sustainable technology for treatment of solid wastes and waste water. Recently, novel plug flow reactor system has been installed at few local institutions to treat semi solid wastes with improved efficiency. However lack of understanding of operational parameters and functional units of this reactor system has led to suboptimal operation and thereby low gas production and methane yield. In this study, plug flow anaerobic reactor is modeled using two modeling scenarios. For this task, Anaerobic Digestion Model No. I (ADM1) implemented in the simulation software package called AQUASIM 2. If is used. Under first scenario, advective diffusive reactor compartment followed by two continuous stirred tank reactors for collection of slurry and gas used to model the plug flow reactor. Under second was scenario, series of CSTR reactors were used to model plug flow reactor and biogas was collected into a common head space via diffusive link. Simulation was performed for the different hydraulic retention times and feed flow rates for the substrate of food waste. Simulation results from advective-diffusive reactor model revealed that accumulation of gasses in the slurry causes an inhibition in methane production. In series of CSTR model, when the food waste alone was used at low hydraulic retention times, pH decreases drastically and causes to process inhibition in the first reactor. This inhibition propagates towards the other connected CSTR reactors and after a certain periods of time total methane production ceases

Effect of pH and external electron donor on mesophilic sulfate reduction during start-up of anaerobic digesters treating skim latex wastewater

Effluent of skim latex industry contains high concentrations of sulfate, together with ammonia, protein and organic matter. This research study investigates the influence of pH and addition of external electron donor on improvement of sulfate reduction in anaerobic digestion under high ammonia concentrations, using Skim Latex Wastewater (SLW) during initial start-up period. Experiment was conducted using two 3- liter reactors fed semi continuously at 35 ±1 ̊C. The influent COD/SO4-2 ratio and the pH of real skim latex wastewater was 2.8 and 5.9 respectively. The experiment was conducted in three phases. During phase I and II, the pH of the reactors was not controlled whereas the influent pH of the sample was adjusted to 7, and influent pH was adjusted to 3 in phase III. The influent COD/SO4-2 ratio was 2.8 in phase I, while in phase II and III it was increased to 10 using acetate. In phase I, average sulfate reduction per cycle was only 33 ± 2 %. When the influent COD/SO4-2 ratio was increased to 10 using acetic acid during phase II, average sulfate reduction per cycle increased to 64%, but it gradually decreased to 30%, 8% and 0% within next three feeding cycles, this is because the pH of the anaerobic digesters increased steeply to 8.85 ± 0.3. Although sulfate reduction increased with addition of external electron donors such as acetate, according to results, the sulfate reduction was adversely affected due to free ammonia formation at the end of the phase II. Sulfur reducing bacteria (SRB) withstand high pH values as 8.8. Even though the anaerobic reactors inhibited, they did not completely fail. But when the Free Ammoniacal Nitrogen (FAN) of the system reached 679.5 ± 12.2 mg/l, the system completely inhibited. The completely inhibited sulfate reduction process was recovered by decreasing the pH of the digester by decreasing the pH of the influent feed sample to 3, while influent COD/SO4-2 ratio was at 10. Thus, sulfate reduction again increased in phase III. In the first cycle of phase III, after the low pH influent fed to the reactors, percentage sulfate reduction per cycle increased to 76%, decreasing the accumulated sulfate in the reactors. But within next three cycles of phase III, average sulfate reduction was 58 ± 3%. When the pH of the digester was controlled at 7.5, the FAN concentration was able to be maintained 92% lower. Thus, the system inhibition could be avoided by controlling the digester pH at 7.5 by controlling influent pH and enhancing sulfate reduction with increasing influent COD/SO4-2 ratio to 10

Effect of lipid inhibition in anaerobic wastewater treatment : a case study using desiccated coconut wastewater

Anaerobic treatment processes have been extensively developed for the treatment of various wastewaters containing high concentrations of organic substrates including proteins, carbohydrates and lipids. The desiccated coconut industry in Sri Lanka is one of the industries where wastewater with high concentrations of lipids containing medium chain saturated fatty acids (~55%), long chain saturated fatty acids (~35%) and long chain unsaturated fatty acids (~10%) is generated. The long chain organic molecules of lipids undergo a series of complex biochemical reactions such as hydrolysis, acidogenesis, acetogenesis and methanogenesis during anaerobic digestion. According to previous studies, high concentrations of lipids have an inhibitory effect on anaerobic treatment processes, due to the mass transfer limitations and toxicity caused by long chain fatty acids (LCFA) towards syntrophic substrate-degrading bacteria. Undesirable effects of accumulation of LCFA in anaerobic reactors comprise of gradual drop down of rate of biogas production and derogatory effects on quality characteristics of effluents such as chemical oxygen demand (COD), biochemical oxygen demand (BOD) and oil and grease removal efficiencies after anaerobic treatment, causing the treatment process inefficient. According to the case study, desiccated coconut wastewater (DCWW) has pH 4.0 - 5.5, COD 4,000 mg/l - 8,000 mg/l, BOD 1,000 mg/l - 5,000 mg/l and total lipids 4,000 mg/l. In anaerobic treatment of DCWW, the COD removal efficiency rapidly changes from 90% - 30% due to the lipid inhibition caused by medium chain and LCFA in DCWW such as lauric acid and myristic acid. The treatment efficiency of anaerobic digestion can be enhanced via different physicochemical strategies