Anaerobic digestion of sewage sludge for enhancing the growth of black soldier fly larvae

Abstract

The growth of black soldier fly larvae (BSFL) has been widely studied by feeding with myriad organic waste materials, transforming the wastes into a high-value added larval biomass via digestion and assimilation processes. One of the abundant organic wastes is a sewage sludge, comprising of complex organic substrates. Nevertheless, the presence of extracellular polymeric substances in the sewage sludge has been found retarding the digestion process of BSFL. As a result, the larvae are unable to assimilate the nutrients for their subsequent growth. In this regard, the anaerobic digestion of sewage sludge was adopted in this work to cleave the structures of sewage sludge in releasing more nutrients for BSFL feeding, whilst enhancing the larval growth. The different pH conditions amidst anaerobic treatment had plausibly changed the quantities of volatile fatty acids generated in which influencing the BSFL growth. The results showed that the larvae fed with the anaerobic treated sewage sludge had a better growth than those fed with fresh sewage sludge in terms of final total weight. The larval weights were measured at 2.05 ± 0.39 against 7.34 ± 0.97 mg/larva at dry weight basis while administering with fresh and anaerobically treated sewage sludge at pH 3, respectively, with an increment of almost 350%. Indeed, the highest larval weight was successfully achieved by using the sewage sludge having been pre-digested anaerobically at pH 3 for 8 days.