Application of Vermifiltration for Domestic Sewage Treatment

*Lubelihle Gwebu and Canisius Mpala*

## **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 nonpotable water uses. Phytoremediation can be incorporated in the designs to increase efficiency.

**Keywords:** biofilters, *Eseinia fetida*, vermifiltration, wastewater treatment, physico-chemical parameters

## **1. Introduction**

Climate change has led to water shortages in arid and semi-arid regions. Sustainable development goal (SDG) 13 on climate change has been set to combat climate change by advocating for wastewater reuse. Zimbabwe depends on conventional sewage treatment systems, which are expensive, centralised, inefficient due to increasing population dynamics, high maintenance and need of high expertise. Countries such as Australia and China have adopted the vermifiltration technique, which combines the filtration process and earthworms in the treatment of sewage water. Vermifiltration is efficient, cost-effective, requires less expertise and

can be decentralised. This study applied the vermifiltration technique on the treatment of domestic sewage water from a septic tank. The aim was to determine the design parameters of a vermifilter, characterising its efficiency in the removal of selected physico-chemical, microbiological parameters and comparing vermifiltered water against the Environmental Management Agency (EMA) irrigation water standards.

### **1.1 Wastewater management**

Reclaimed water is a product of treated wastewater that includes industrial and domestic effluent [1]. Wastewater treatment is a technique for sewage water management. It involves the removal of pollutants in wastewater that are a threat to the environment. It involves chemical, biological and physical processes for the removal of the pollutants in water using infiltration systems, trickling filters, wastewater stabilisation ponds and septic tanks. One of the main products is reclaimed water and sludge that is deposited into the environment [2].

The use of conventional systems for the treatment of wastewater is costly, requires high maintenance, is centralised and has no resource recovery of reclaimed water. However, some countries have adopted vermifiltration as an alternative method for the treatment of wastewater [3].

### **1.2 Vermifiltration**

Vermifiltration is a wastewater treatment method that incorporates the use of earthworms and the infiltration system [4]. The earthworms act as bio-filters and are capable of degrading, digesting and decomposing organic waste [5]. This is achieved through promoting growth of beneficial decomposing bacteria, biological stimulation, aeration and chemical degradation. Studies have shown the efficiency of vermifiltration in controlling pH, chemical oxygen demand (COD), total dissolved solids (TDSs), biological oxygen demand (BOD5), turbidity and chlorides (Cl) [4, 6]. It was first established at a University in Chile by Professor Jose Toha in 1992 [7]. Other countries are now using the treatment system, and it has been recommended for developing countries [4].

It is an efficient, inexpensive technique, non-labour intensive, requires low expertise, can be decentralised and is environmentally friendly. One of the products is reclaimed water that can be used for irrigation, landscaping, fire protection, flushing and vermicompost [1, 6]. Therefore, this study intended to recover the wastewater for non-potable water uses through the application of vermifiltration for domestic sewage treatment from septic tanks at Lupane State University (LSU).

LSU and Lupane Town do not have any wastewater treatment plant that enables the access of reclaimed water. Septic tanks are used for wastewater treatment, and thus, there is no use of either recycled or reclaimed water. The university uses approximately 30,000 litres of water per day from the hostels and the dining hall that goes to the septic tanks, and it is not reused. The use of septic tanks could also contribute to the pollution of underground water and contamination of the soil. The wastewater treatment plants currently used in Zimbabwe need high maintenance. With the growing population at the LSU campus, there will be decrease in the treatment efficiency of the septic tanks due to overload [8, 9].
