Dear Emmanuel Amagu,

Cassava waste water contains high concentrations of easily acidifying compounds, requiring a buffered system to allow a stable operation during anaerobic digestion (AD). The possibility to include a preliminary one-step fungi treatment aimed at raising the pH and buffering the cww prior to AD was studied. Preliminary tests were performed with a naturally grown fungal mixed culture, under aerated (AE), non-aerated (NAE) and initially oxygen-deprived (IOD) conditions. The cww was pre-treated by the NAE condition, until reaching a soluble chemical oxygen demand (COD) of 10 g L−1and pH 6.4 (batch A) and pH 5.7 (batch B). The fungal mixed culture showed ability to biodegrade the cww with initial pH of 4.4 and 14,500 mg COD L-1, raising the pH over 8.5, with only 13 % of COD remaining within 27 days for both AE and NAE condition. The fungal pre-treated-cww (FPTcww) was subjected to anaerobic digestion under different buffered (CaCO3 and NaHCO3) and non-buffered conditions. The FPTcww with initial pH at 6.4 provided stability during the anaerobic biodegradability tests, showing the possibility of system operation without buffer addition, with final pH around 7. The application of a fungal pre-treatment can be a promising strategy to permit the anaerobic digestion of carbohydrate-rich waste waters.

please find attached herewith related articles,

regards,

Prem Baboo

Dear Prem Baboo,

Thanks. Your answer and suggested links are quiet useful. 

Dr. Emmanuel Echiegu 

Dear Emmanuel,

I agree with Prem that cassava/tapioca wastewater readily acidifies in facultative anaerobic conditions. However I would not recommend aeration as suggested by Prem upstream of anaerobic digestion because residual oxygen would be more toxic to the methane producing archaea than the natural cyanide from the cassava root. We have plenty of full-scale experience in methanizing cassava wastewater and we achieve up to 95% COD conversion without adding any chemicals except for a bit of lye for partial neutralisation of the acidified wastewater.

I would like to add that aeration - including mixing by air as applied in India and in other countries - of acidified wastewater would also strip out volatile organics which would otherwise be directly converted to methane by anaerobic digestion resulting in lower methane yield.