Bionor sewage sludge technology – Biomass to fertiliser and a soil addition

Abstract

Wastewater treatment plants play a key role in preserving the resources of the environment, as well as human health. The applied technological system of a wastewater treatment plant determines the efficiency of wastewater and sewage sludge treatment, but also energy efficiency and operating costs. The aim of the presented work is to analyse the technological unconventional system of a small wastewater treatment plant with some modifications generating ecological profits, mainly the fertiliser, biomass or peat substitution (“biosolids factory” concept). The modification of the technological system consists in the application of sewage microfiltration, conditioning of sewage and sludge with cellulose material and application of short-term thermo-composting (Bionor technology). The use of a belt filter for suspension separation reduces the load on activated sludge bioreactors and aerobic stabilisation. The basic modification is the use of thermo-composting of separated sewage sludge with the addition of a structure-forming agent (straw pellet). Importantly, no precipitating or flocculating chemical substances or agents are used in this technology. The technology used enables the processing of sewage sludge into biomass with high fertilising and energy potential. In the following work, the Life Cycle Assessment (LCA) of a wastewater (and sewage sludge) treatment plants was made, comparing different possible concepts of sewage sludge management. The LCA was performed on five applied sewage sludge treatment scenarios: incineration of biomass (S1); biomass as a fertiliser product – “fertiliser substitution” (S2); biomass as a soil addition - “peat substitution” (S3); biomass as both fertiliser and a soil addition - “fertiliser and peat substitution” (S4); and biomass as a filling without any substitution benefits - “no specific use” (S5). The LCA analyses of the Bionor sludge technology applied in the wastewater and sewage sludge treatment plant confirm the environmental benefits and minimise the environmental impact with conventional solutions. The fertiliser and peat substitution scenario cause the least impact on climate change. This scenario was found as beneficial for avoiding net CO2 emissions (−5.8 kg CO2 eq/1 m3 wastewater) and eutrophication potential (−1.7 to −2.0 kg N2O eq/1 m3 wastewater, −2.78 to −3.0 PO4 eq/1 m3 wastewater). The eco-toxicity study also showed low impact potentials for a land application scenario. Incineration of biomass yields higher environmental impacts than any application scenario (13.8 kg CO2 eq/1 m3 wastewater). The LCA analysis confirmed that the peat substitution scenario was found as the most valuable.