Treatment of wastewater using Black Soldier Fly larvae: Effect of organic concentration and load

Recent studies have investigated the use of Black Soldier Fly (BSF) larvae as a promising biological treatment process for high organic content wastewater (i.a. Leachate from municipal solid waste landfill, food processing effluents), achieving both high treatment efficiency and production of secondary resources from larval biomass (i.a. Proteins and lipids). The present study was aimed at achieving a better understanding of how organic concentration and load might influence treatment performance. Larvae were fed with three artificial wastewaters characterised by same organic substances quality (degree of biodegradability and oxidation of the organic content measured respectively as BOD/COD and TOC/COD ratios) but different organic concentrations. Each type of wastewater was tested at four different loads. Treatment performance was assessed by monitoring both larval growth (in terms of weight variation, mortality and prepupation), and variation of wastewater quality and quantity to determine organic substrate consumption (measured in terms of Total Organic Carbon, TOC). Larval starvation was observed in all tests when TOC concentrations dropped below approx. 1000 mg C/L, which, for the tested wastewater, could be assumed as the limit value for adopting BSF larvae process. Substrate concentration in the feed (mgC/L) influenced larval growth (in terms of maximum wet weight, prepupation and mortality) only when organic load was above 10 mgC/larva: the higher the load, the higher the positive impact of the substrate concentration. On the contrary, the specific substrate consumption rate (v_S, mgC/larva/day) appeared not to be influenced by substrate concentration but only by the organic load, with a Michaelis Menten like relationship. Accordingly, substrate load can be assumed as a design parameter for BSF treatment process, while substrate concentration might only influence potential resource recovery from larval biomass.