Thermophilic composting of hydrocarbon residue with sewage sludge and fish sludge as cosubstrates: Microbial changes and TPH reduction

Abstract

The hydrocarbon residue in petroleum product storage tanks is waste generated in large quantities that must be properly managed to reduce its risk to the environment. By comparing the effect of two organic cosubstrates, the aim of our research is to determine the feasibility of composting as a bioremediation method for the treatment of the solid phase of the hydrocarbon residue. For this purpose, four treatments of the pollutant waste were established in triplicate: waste only; waste with bulking agent (1:2); waste with fish sludge and bulking agent (1:2:6); and waste with municipal sewage sludge and bulking agent (1:2:6). The composting system consisted of 12 reactors with a capacity of 30 L, each equipped with aeration and temperature control. Both at the beginning and the end of the experiment (20 days), we evaluated the physicochemical parameters, the structure of the microbial community through phospholipid fatty acid analysis, and the total petroleum hydrocarbon content (TPH). Treatments with cosubstrates maintained thermophilic temperatures, during 14 and 8 days in fish and municipal sludge respectively, while in the controls mesophilic conditions were maintained. The incorporation of fish sludge decreased TPH present in the initial mixture by 39.5%. The municipal sludge treatment resulted in a lower of temperatures and a TPH decrease close to 23.9%. In the control treatments, there was a slight TPH decrease, mainly due to the forced ventilation. Although, both composting treatments with cosubstrates proved adequate for the bioremediation of residue from hydrocarbon storage tanks, fish sludge presented best bioremediation conditions. Municipal sewage sludge provided a bioaugmentation effect due to its rich diversity and microbial biomass. Fish sludge could have biostimulant and surfactant effect producing an aliphatic mixture of pollutant waste with the nutritional requirements to promote the development of fungal communities.