Improved Agro-Industrial Waste Utilization in Biogas and Fertilizer Production Ensuring Co2 Sequestration

The global food crisis approach encourages finding new sources of replenishment of the phosphorus deficit in agriculture. Today, unconventional sources of phosphorus, such as sewage activated sludge from municipal wastewater, becoming particularly relevant, but despite numerous studies of phosphorus recovery methods, the need to increase the content of nutrients in the resulting products still exists. The greatest success in this area has been achieved by the biotechnologies which ensure the simultaneous production of biogas and biofertilizers. The present study proposes a sustainable technology for anaerobic digestion with the simultaneous capture of carbon dioxide and sodium carbonate production. It involves pre-comminution of the organo-mineral substrate (vegetal waste, activated sludge, phosphorus-containing component, and cheese whey) facilitating anaerobic digestion, and extraction of CO2 from biogas by absorption with a 10% NaOH solution. Biomethanation reaction was found to have the first order, its activation energy is 24.8 kJ/mol, whereas the carbon dioxide absorption degree is proportional to the CO2 content in biogas. The results showed good potential for increasing the efficiency of both phosphorus recovery from municipal wastewater, and anaerobic digestion to produce valuable products, including high-purity bio-methane (96 vol.% CH4), concentrated (∑NPKCa 53%) organo-mineral fertilizer from digestate, and soda ash. The increase in potato yield when using the resulting fertilizer was 35 wt.%. The study demonstrates a novel concept of carbon dioxide cycle looping in biogas production, as well as reducing greenhouse gas emissions by converting up to 98.7% of CO2 into an additional marketable product – sodium carbonate, which contains 99% Na2CO3