Using Vermifiltration Technology in Biocleaning of Raw Urban Wastewater and Improving Quality Characteristics of the Effluent

Introduction
Iran is currently facing a serious and growing water scarcity crisis. Efficient water resource management has therefore become essential, and wastewater treatment and reuse are among the most effective strategies for mitigating water shortages and improving water-use efficiency. Municipal wastewater consists of approximately 99.9% water and only about 0.1% impurities; however, this small fraction includes a wide range of pollutants such as biodegradable organic matter, suspended solids, nutrients, pathogens, heavy metals, refractory organic compounds, and dissolved solids. Untreated wastewater discharge into surface and groundwater bodies can cause severe environmental pollution and public health risks. Proper wastewater treatment is therefore necessary not only to prevent disease transmission and protect water resources but also to enable the safe reuse of treated effluent for agricultural irrigation, aquaculture, and environmental conservation. Conventional wastewater treatment methods include physical, chemical, and biological processes. Physical and chemical methods are often expensive, energy-intensive, and sometimes inefficient in removing target pollutants. In addition, these systems usually generate large amounts of sludge, which creates significant operational and disposal challenges. Biological treatment systems have gained increasing attention due to their lower cost and environmental compatibility. Among these, vermifiltration has emerged as a promising, sustainable, and low-cost biological technology. Vermifiltration is a natural bio-oxidative process that integrates earthworms and microorganisms to enhance the degradation of organic pollutants while minimizing sludge production. This study aimed to evaluate the efficiency of vermifiltration for municipal wastewater treatment in Alborz province, Iran, and to assess the suitability of the treated effluent for agricultural irrigation.
 
Methodology
Cattle manure was collected from the educational–research farm of the College of Agriculture and Natural Resources, University of Tehran, located in Mohammadshahr, Alborz province. The manure was washed, air-dried, and mixed with chopped dry leaves at a ratio of 1:2 (manure: leaf litter). The mixture was inoculated with compost earthworms (Eisenia fetida) obtained from a vermiculture facility in Amol Mazandaran province, Iran. Approximately 1000 earthworms were introduced into ventilated plastic containers, which were maintained at about 25 ^°C and 60% moisture content for one month to produce young vermicompost.Three plastic reactors with a capacity of 100 L were constructed for wastewater treatment. Each reactor consisted of a layered filter bed comprising gravel (15 cm), fine sand (10 cm), and clay soil (5–10 cm), topped with a 50 cm layer of prepared vermicompost. Raw municipal wastewater was collected from the influent of the Hashtgerd wastewater treatment plant and transferred to the laboratory. The experiment was conducted under three operational modes: (1) continuous flow, (2) intermittent flow with a 6-hour retention time, and (3) intermittent flow with a 12-hour retention time. Wastewater was applied to the systems over an eight-week period with three replications, and effluent samples were collected weekly. Influent and effluent samples were analyzed for pH, electrical conductivity (EC), total dissolved solids (TDS), total suspended solids (TSS), biochemical oxygen demand (BOD₅), chemical oxygen demand (COD), total bacterial count, and fecal coliforms (MPN method). Data were analyzed using SAS software (version 9.4) in a split-plot design over time. Means comparison was performed using Duncan’s multiple range test at 1% and 5% probability levels.
 
Results
The analysis of variance indicated that the mode of wastewater application had a highly significant effect (p< 0.01) on all measured physicochemical and biological parameters. Time also had a significant effect on several parameters, including pH, EC, TDS, and TSS, and also significant interaction effects between system type and time were observed. The pH of the treated effluent was decreased after passing through the vermifiltration systems and gradually stabilized within the neutral range, reflecting the buffering capacity of earthworms and their associated microorganisms. Electrical conductivity was initially increased due to the relatively high salinity of the vermicompost bed but showed a decreasing trend over time. Significant reductions in TSS and TDS were observed in all vermifiltration systems, with the continuous-flow system showing the highest removal efficiency. These reductions can be attributed to the ingestion and fragmentation of suspended particles by earthworms, enhanced microbial activity, and physical filtration within the filter media. Biological parameters showed substantial improvement following vermifiltration. Both total bacterial counts and fecal coliform populations were significantly reduced, particularly in the continuous-flow system. Pathogen reduction is mainly attributed to earthworm digestion, improved aeration, competition with beneficial microorganisms, and exposure to antimicrobial secretions produced by earthworms and associated microflora. Overall, the continuous-flow vermifiltration system demonstrated superior performance in reducing BOD, COD, TSS, TDS, and microbial indicators compared to intermittent systems.
 
Conclusions
This study demonstrated that vermifiltration is an effective, low-cost, and environmentally friendly technology for municipal wastewater treatment in arid and semi-arid regions. Among the evaluated treatments, the continuous-flow vermifiltration system showed the highest overall efficiency in improving the physicochemical and biological quality of treated effluent. Most measured parameters, including pH, TSS, BOD₅, COD, and fecal coliforms, met national and international standards for agricultural irrigation. Although EC and TDS values exceeded recommended limits due to the characteristics of the vermicompost bed, the overall quality of the treated effluent was significantly improved. Given its simple design, low energy requirements, minimal sludge production, and high treatment efficiency, vermifiltration represents a promising and sustainable option for wastewater management and reuse in water-scarce regions such as Iran.
Author Contributions
Conceptualization, H.A. and A.L.; methodology, H.A. and A.L.; software, H.E. and S.S.; validation, H.A., A.L., H.E., and S.S.; formal analysis, M.E. and S.S.; investigation, M.A.; resources, H.A. and M.E.; data curation, H.A. and A.L.; writing—original draft preparation, S.S. and M.E.; writing–review and editing, S.S., H.A., and M.E.; visualization, H.A. and A.L.; supervision, H.A.; project administration, H.A.; funding acquisition, H.A. All authors have read and agreed to the published version of the manuscript.
Data Availability Statement
Data is available on reasonable request from the authors.
Acknowledgements
The authors are thankful to the University of Tehran for financial supports.
Ethical considerations
The authors avoided data fabrication, falsification, plagiarism, and misconduct.
Conflict of interest
The author declares no conflict of interest.