Improved agro-industrial waste utilization in biogas and fertilizer production ensuring CO2 sequestration

Abstract

The global food crisis approach encourages finding new sources of replenishment of the phosphorus deficit in agriculture, making the unconventional sources of phosphorus particularly relevant. Despite numerous studies of phosphorus recovery methods, the need to increase the content of nutrients in the organo-mineral fertilizers obtained via anaerobic digestion of sewage activated sludge from municipal wastewater 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 with the activation energy of 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. Obtained fertilizer increased potato yield by 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.