Modelling anaerobic digestion of concentrated black water and faecal matter in accumulation system

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A dynamic mathematical model based on anaerobic digestion model no. 1 (ADM1) was developed for accumulation (AC) system treating concentrated black water and faecal matter at different temperatures. The AC system was investigated for the treatment of waste(water) produced from the following systems: vacuum toilet for black water (VBW), vacuum toilet for faeces with urine separation (VF), dry toilet (DT), dry toilets for faeces with urine separation (DF), separated faecal matter from conventional black water by filter bag (FB). For evaluation of the AC system treating the proposed waste(water) sources at 20 and 35 °C, two options were studied: (1) The filling period of the AC system was constant for all waste(water) sources (either 1, 3 or 6 months) and for each period, the seed sludge volume was varied; (2) The volume of the AC system was constant for all proposed waste(water) sources. The results showed that the filling period of the AC system was the main parameter affecting the system performance, followed by operational temperature, while the increase of the seed sludge volume slightly enhanced the performance of the system. The model results indicated that the filling period of the AC system should be higher than 150 days for obtaining a stable performance. It was found that the hydrolysis of biodegradable particulate chemical oxygen demand (COD) is the rate limiting step, as volatile fatty acid concentration is very low in all experimental conditions (<200 mgCOD/L at 20 °C and <100 mgCOD/L at 35 °C). Based on the results of the two options, it was found that the concentrated waste(water) sources have better performance than the diluted waste(water) sources, like VBW waste(water). Furthermore, smaller volume will be required for the AC system.

Keywords: accumulation system, anaerobic digestion, black water, domestic wastewater, sustainable sanitation, vacuum toilets

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