On-site sanitation systems such as dry pit, flush Pit, dual pit-latrines and septic tank are widely used around the globe. Due to the absence of any effective technology for the treatment of the septage generated from these sanitation systems, in most of the cases the contaminated septage is dumped in landfills or dumping yards without any treatment. There has been as such no effective development of Faecal Sludge treatment technology to ensure safe fate of the contaminated septage and in most of the occasion they have been found crudely disposed off in landfills or dumping yards and left untreated. The septage or its leachate has potential to cause serious health effects when drinking water gets contaminated. This extended abstract reports some of the results obtained when we employed black soldier fly larvae (BSFL) as a biological agent for the treatment and reduction of the amount of fresh human feces which forms a part of the septage. BSFL is a voracious eater of organic wastes and has been reported in literature to be very efficient agent for waste reduction and conversion into their body weight (Diener at al. 2011, Banks et al. 2014, Paz et al. 2015). Generally, the BSFL has a larval life of 14 days during which they consume food and gain weight before they turn into a prepupae wherein they avoid food. They turn into pupae and eventually, in a fly. Just like many other biological agents, these larvae are sensitive to environmental conditions such as temperature and humidity so that the most efficient waste reduction may take place at an optimum temperature and humidity. In this research our objective is to study the effect of the environmental parameters such as temperature and humidity on the substrate (human feces) reduction and weight gain by the BSFL. We performed a set of experiments involving BSFL put in fresh human feces under different environmental conditions. The temperatures were 25, 30 and 35 deg C which is within the prevailing temperature range (25-35 deg C) in most parts of India. For each temperature, relative humidity (RH) was varied between 55-85%. For each experiment, 50 numbers of 6 day old larvae were kept inside a box inside which 200 g of fresh human feces collected from a septic tank was spread at 2 cm thickness. Three replicates (human feces and BSFL) along with control (only contains human feces and no larvae) were made and each box was maintained at specific temperature and relative humidity inside an incubator. The BSFL as well as the substrate were weighed every other day till they kept on gaining weight. Figure 1.1 shows the Percentage weight gain of the BSFL and Percentage reduction in the substrate for the experiments run at 30 deg C and at different levels of relative humidity as an example. Due to brevity, we have included only the results obtained from the experiments run at Temperature,T=30 deg C and Relative Humidity (RH)= 55, 65, 75 and 85%.
The substrate reduction was found to be in the range of 3-17%, the highest being at RH of 65-75%. The weight gain of BSFL was observed to be in the range of 39-91%, the highest being at 85% RH. The results indicate that at 300C, the optimum utilization of food takes place at 65-75% RH. However, larval weight gain follows a different trend, monotonously increasing with respect to the relative humidity. The logical inference is that the larvae are most active in feeding as well as metabolising (catabolising) the substrate at RH of 65-75 %, while at higher RH the feeding rate is lower and the rate of metabolism (catabolism) is even lower. The weight gain of BSFL per unit substrate reduction for each larvae at RH=55, 65, 75 and 85% was calculated as 1.521, 0.983, 1.361 and 2.031 mg/gram. Hence, there is a net gain in weight of the BSFL at high humidity where, due to reduced activity, they cannot catabolize even the food they consume. As a result, there is a weight gain, which may at once look as anomalous result. The substrate consumed by each larvae was 0.613, 0.666, 0.656 and 0.579 g at RH=55, 65, 75 and 85%, respectively. This means that approximately 1500 numbers of BSFL may be required to consume 1 kg of human feces at 65-75% RH. Overall, BSFL showed a promising agent for the treatment of fecal sludge management.