6.4 What are the residue characteristics of FS treated by BSFL?

Sludge and Biosolid Management 6 Black Soldier Fly Larvae Treatment 6.4 What are the residue characteristics of FS treated by BSFL?

The use of BSFL in the treatment of faecal sludge (FS) is a relatively novel concept and has not been explored to the extent of other conventional treatment methods. The optimal conditions for effective FS degradation, such as larval density, moisture content, and feeding rate are still undefined.

A study to explore the performance and effectiveness of BSFL in treating FS from pit latrines in informal settlements in Kampala City, Uganda was carried out by collecting and examining FS samples from lined and unlined pit latrines before and after BSFL treatment.

To further explore the influence of BSFL in the degradation process, control experiments of FS from the pit latrines were set up under similar conditions but without BSFL.

The following table shows the characteristics of the residues of FS from the lined pit latrines as an average, before and after BSFL treatment. Also included are some suitable ranges of various parameters for the breeding of BSFL, established by the study.

Parameter	Unit	Faecal Sludge Before BSFL Treatment	Residue After BSFL Treatment	Control	Condition Suitable for Breeding BSFL
pH	–	7.40	8.54	8.10	5.25 – 8.94
Moisture content	%	90.20	59.40	59.55	40 – 90
Total solid	g/L	128.60	0.50	0.70	133 – 480
COD	mg/L	90,667	92.80	99.97	50,000 – 150,000
TN	mg/L	2009	1.80	1.67	–
TP	mg/L	1605	2.14	2.18	–
Helminth eggs	No. per g	250	27	16	–
Cu	mg/L	84.60	0.15	0.12	–
Mn	mg/L	32.30	0.43	0.49	–
Zn	mg/L	414.60	0.34	0.54	–
Cd	mg/L	1.20	0.003	0.002	–
Cr	mg/L	5.20	0.03	0.03	–
Pb	mg/L	31.60	0.05	0.03	–
Hg	mg/L	0.00	0.00	0.00	–

Characteristics of residues of faecal sludge from lined pit latrines before and after BSFL treatment in Kampala City, Uganda (R. Tokwaro, 2023)

It can be observed from the table that BSFL application resulted in notable differences between some of the residue characteristics from the lined pit latrines and its corresponding control group.

Firstly, BSFL application resulted in a significant increase in the residue pH. This can be explained by the fact that ammonia is produced from organic nitrogen during the decomposition process, and the ammonia acquires hydrogen ions from the water to produce hydroxide ions, which in turn causes an increase in pH (Lalander et al., 2014).

The lower COD levels in the residue can be attributed to the fact that BSFL accelerates the decomposition of organic matter.

Concerning pathogen removal, BSFL have been reported to be effective in removing E. coli and salmonella (Siddiqui et al., 2022).

However, there was no significant reduction in the amount of helminth eggs in the residue with and without BSFL, which implies that there is a need for further treatment of the residue if it is intended to be used as compost in agriculture.

BSFL are capable of reducing FS volume by about 60 – 80% and has the potential to effectively treat it under the right conditions. As shown by the aforementioned study, FS with moisture content as high as 90% can be treated with BSFL. This establishes that they can be applied in the treatment of FS from informal settlements without the need for a prior dewatering step.

In conclusion, employing BSFL for FS treatment can significantly reduce the FS volume whilst producing a nutrient-rich residue of good quality to use as agricultural compost, given that the residue is further treated to reduce the helminth egg count prior to use.

For further information, please click on the Materials tab at the top of the page.

Further Reading:

Application of black soldier fly larvae in decentralized treatment of faecal sludge from pit latrines in informal settlements in Kampala city

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