**4.5 Comparison of effluent with EMA guidelines (SI 6 of 2007 on effluent and solid waste disposal)**

**Table 5** shows that the domestic sewage from the septic tank was not within the EMA standards for effluent disposal except for pH and nitrates.

## **4.6 Discussion**

### *4.6.1 Change in chemical parameters of the wastewater*

There was a decrease in the pH, phosphates and BOD after treatment in both the VF and CF. An increase occurred in the level of nitrates after treatment.

*Application of Vermifiltration for Domestic Sewage Treatment DOI: http://dx.doi.org/10.5772/intechopen.103920*


*The EMA Statutory Instrument 6 on Irrigation water standards uses the colour codes blue, green, yellow and red to indicate the level of pollution. Hence the colour shows whether the parameter is with the permissible limits or not.*

### **Table 5.**

*Sewage quality parameters for disposal of the effluent relative to EMA standard guidelines.*

### *4.6.2 pH*

The pH of the untreated domestic sewage was within the EMA standards. It is due to the decomposition of organic matter that occurs in the septic, thus reducing acidity and alkalinity of the domestic sewage. The treated sewage both from water from the CF and VF had a pH range that decreased though it was within the EMA standards. These results in the CF were due to the biological reactions that occurred through the infiltration process. The pH of the vermifilteted water drew closer to neutrality due to the vermicasts produced by the earthworms which are more neutral. Similar results were obtained by [4, 6].

### *4.6.3 Phosphates*

Analysis of variance revealed that the biofilters were significantly efficient in treating the domestic sewage. The decrease in phosphates in the VF is attributed to the availability of anoxic conditions, biological metabolism and iron corrosion. The earthworms accumulate phosphate in the gut system, hence reduce the level of phosphates in the water.

### *4.6.4 Nitrates*

The analysis of variance results showed that there was a significant difference in the untreated sewage and the treated sewage using the VF and CF. However, a significance difference also existed within the two filters. Generally, the nitrates in raw sewage are supposed to decrease during the treatment as they are supposed to be converted from nitrate and further decomposed to nitrogen gas and water through the nitrification and denitrification processes. The CF and VF had an increase in nitrates due the removal of ammonia through adsorption which leads to the formation of nitrates through biological nitrification. The earthworms also have a lot of nitrifying and denitrifying bacteria in the gut of worms.

Therefore, the presence of oxygen, aerobic *Nitrobacter* and the worm cast oxygenates the influent, thus leading to the increase of nitrates [34]. The nitrates formed are, however, made available to the plants. This is due to the secretion of polysaccharides, proteins and other nitrogenous compounds; these mineralise the nitrogen and make it available to the plants [35]. Similar results were obtained by [6, 9].

### *4.6.5 Bod*

Vermifilter was significantly effective in reducing BOD which is attributed to the absorption of the organic waste by the worms through their body wall and the uptake through their gut. There is high effective symbiotic relationship between the earthworms and the soil microbes. They accelerate and increase the rate of decomposition of the organic matter [36, 37]. The muscular action of the foregut of the earthworms plays a crucial role. The organic matter is degraded, homogenised, conditioned, and biological activity in filter is improved. A decrease in BOD in the control filter is due to the filtration process and the action of bacteria that grow in the filter as well as the presence of the biofilm that is formed.

### *4.6.6 Decrease in physical parameters*

There was a significant difference in all the selected physical parameters on the untreated and treated sewage after experimentation.

### *4.6.7 Turbidity*

The analysis of variance results revealed that the vermifilter and the control filter were effective in treating domestic sewage. The decrease in turbidity is due to the adsorption of both the macroscopic and microscopic suspended solids in the filters. The adsorption occurs in the soil and gravel. The VF was more efficient due to the role of earthworms. The earthworms feed on the organic matter, thus reducing organic waste and proportionally controlling turbidity.

### *4.6.8 Total dissolved solids*

The vermifilter and the control filter had a significant effect on the treatment of TDS in the domestic sewage water. The VF and CF water were within the EMA standards. The decrease of the TDS in the VF is attributed to the ingestion of the organic and inorganic solid particles in the RW by the earthworms. The earthworms excrete finer particles. The TDSs both in the CF and VF are trapped through adsorption and stabilised during the infiltration process [38].

### *4.6.9 Total suspended solids*

There was a significance difference in the total suspended solids in untreated and treated sewage. A decrease in the CF is a result of the TSS sticking on the surfaces of individual filter media such as gravel and sand through adsorption and trapping of the suspended solids [39]. The removal of TSS in the VF was more effective as the TSS trapped on the filter reprocessed by the earthworms and fed to the microbes in the soil for further decomposition. Earthworms burrow within the soil and this increase aeration, thus enhancing efficient filtration and soil stabilisation [29].

### *4.6.10 Change in the total coliforms*

The coliforms decreased in the VF due to the ability of earthworms to release coelomic fluids. These fluids have antibacterial properties and are capable of destroying all the pathogens in the biomass. The earthworms ingest the organic matter which they process through culling up the harmful microorganisms. The end products are deposits which are mixed with minerals and beneficial microbes free from pathogenic particles in the soil [39]. The decrease is also attributed to gizzard and intestinal enzymes of the earthworms. They are secreted through their body wall [40]. The decrease in the CF of total coliforms was due to the action of the biofilm that destroys the bacteria in the wastewater.

### **4.7 Conclusion**

The water from the VF and CF was both within allowable limits of the SI 6 standards by EMA, except for the nitrates and turbidity. Total suspended solids were in the blue allowable range in the VF, whilst in the CF it was on the yellow range which is a threat to the environment. The vermifilter met the blue and yellow allowable limits that are even permissible for irrigation. The vermifiltered water can therefore be used for irrigation of parks and landscaping.

The vermifilter and the control filter were both effective in treating the domestic sewage from the septic tank. All the physicochemical and microbiological parameters were within the EMA regulation standards for disposal. They ranged between the blue-yellow range of acceptance. However, the most effective filter was the vermifilter.

The control filter is not sustainable since with time it clogs, discharge of effluent rate lowers and there was a foul smell. It is rich in nutrients that are nitrates and phosphates that are in an available form to the plants. There is a potential for the recycling of the sludge in the septic for use as manure and production of biogas.

The study shows that there is a potential for the recycling of the sludge in the septic for use as manure and production of biogas. It is recommended to carry out water quality assessments on borehole water and soil to see if there is any contamination as a result of the use of septic tanks.

Design improvement of the vermifilter can be done by incorporating phytoremediation as to increase treatment efficiency as to control the increase in nitrate concentration.

## **Acknowledgements**

The authors appreciate the assistance given by Mr. R. Mudziwapasi for guidance in the experimental setup; Mr. E. Ndlovu for data analysis; L. Musaradenga, Mr. T. Kachote and Miss G. Dube, who assisted in laboratory analysis. Thanks to Mr. D. Sibanda and Mr. C. Moyo from the Works and Physical Planning Department for the provision of designing tools and their assistance.

### **Conflict of interest**

The authors declare no conflict of interest.

*Wastewater Treatment*
