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65% confidence

This study applies vermifiltration—a biofilter system combining earthworms (Eisenia fetida) with layered soil media—to treat domestic sewage from septic tanks in Zimbabwe. The system achieved significant reductions in BOD (68–98%), turbidity (77–99%), total suspended solids (24–97%), phosphates (90–99%), and total coliforms (78–98%) at a hydraulic retention time of 1 hour 40 minutes and loading rate of 163 L/m²/h. Vermifiltered effluent met Environmental Management Agency standards for irrigation and non-potable reuse, demonstrating potential for decentralized wastewater treatment in semi-arid regions.

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Abstract

Climate change has led to water shortages in semi-arid regions. SDG 13 was advocates for wastewater reuse. Zimbabwe uses centralised conventional sewage treatment systems. Vermifiltration combines filtration process and earthworms in sewage water treatment. Vermifiltration is efficient, viable, requires less expertise and can be decentralised. Vermifiltration technique was used in treating domestic septic tank sewage water. Design parameters and efficiency were determined and characterised Vermifiltered water parameters were compared against the Environmental Management Agency Statutory Instrument 6 irrigation water standards. Vermifilter media contained gravel and composted soil with 20g Eseinia fetida earthworms per litre of soil. Treatments were septic tank raw water, vermifilter and control biofilter. A duplicate analysis was conducted. Hydraulic retention time was 1 hour 40 minutes and hydraulic loading rate 163l/m²/hour. Disposed wastewater did not meet required EMA standards. Both filters were effective in treating domestic sewage. There was a significant difference between untreated and treated wastewater. Vermifilter and the control, significantly (p < 0.01) treated pH, turbidity, total dissolved solids total suspended solids, biological oxygen demand, nitrates, phosphates and total coliforms properties. Vermifiltered water met EMA standards for irrigation and non-potable water uses. Phytoremediation can be incorporated in the designs to increase efficiency.

Keywords

Septic tankSewageWastewaterEnvironmental engineeringSewage treatmentTotal suspended solids

Identifiers

DOI
10.5772/intechopen.103920
Journal
Wastewater Treatment
Year
2022