Improvement of pH Prediction Module in Anaerobic Digestion Model No: 1

Description:Nowadays, organic waste management facilities are targeted by regulators for reducing waste and greenhouse gas emissions. Anaerobic digestion is an increasingly popular method to produce biogas/nutrient-rich soil conditioner from waste. Anaerobic Digestion Model No: 1 developed by the International Water Association form the basis of the digestion models in the literature. In ADM1, pH is a key parameter which critically affects the metabolic activity of methanogens. However, ADM1-based models do not include the effect of ionic strength in pH calculations. This leads to inaccurate digester pH predictions by 0.3-0.7 units. Furthermore, when digester pH drops below 4, it becomes unreliable to simulate other parameters, such as volatile fatty acids (VFAs). The objective of the present wok was to identify and analyze the key ions (anions and cations) in digester substrate to achieve more accurate pH prediction. For simulation, sensitivity analysis, and parameter estimation tasks, AQUASIM 2.0 computer program was used. Data were obtained from a full-scale dairy farm digester (ON, Canada) with volume and hydraulic retention times of 500 m3 and 25 days, respectively. Influent composition of the feed substrate was analyzed in terms of key ions such as, ammonium (NH4+), bicarbonate (HCO3-), acetate (CH3COO-), propionate (CH3CH2COO-), butyrate (CH3(CH2)2COO-), K+, Mg2+, Na+, Ca+2, and CO32-. Two stoichiometric equations in the ADM1 were revised. The advanced pH module significantly improved the digester pH prediction (from R2 = 0.82 to R2 = 0.97), obtaining also good agreement between predicted and experimental data for biogas, and VFA concentrations (R2, R2a = 0.92).

Authors: Yang, Danmei; Strehler, Benjamin; Eskicioglu, Cigdem; Crolla, Anna; Allen, Claire

Subjects: Wastewater, Residuals and Biosolids

Tags:digestion,biogas,anaerobic,ac2012

Citation:2012 BCWWA Annual Conference, Session 8, Penticton

Publication Date:Aug 7th, 2012 Upload Date:Aug 7th, 2012

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