Effectiveness of vermifiltration systems in wastewater bioremediation: a sustainable and cost-effective approach

Effectiveness of vermifiltration systems in wastewater bioremediation: a sustainable and cost-effective approach Alexandra Guanuchi, Daniel Aguado and Yolanda Moreno Instituto Universitario de Ingeniería del Agua y Medio Ambiente (IIAMA), Universitat Politècnica de València, Camino de Vera s/n, Valencia, 46022, Spain (E-mail: [email protected] ; [email protected] ) (E-mail: daagga[email protected].es, [email protected] ) Abstract In areas with limited access to conventional sanitation systems, as in rural areas, there is an imperative for sustainable alternatives for wastewater treatment. This study aims to demonstrate the efficiency of a domestic scale vermifilter system containing Eisenia foetida worms and coconut fibre as a substrate in reducing wastewater pollutants. The study evaluated 3 configurations: a filter without worms (control), a vermifilter with 15 cm of coconut fibre and another with 30 cm of coconut fibre. The last one was installed in a house in Baños district of Cuenca, Ecuador. The results showed that the vermifilter with 30 cm of coconut fiber showed the optimal efficiency, achieving removals of 55.8% for COD, 56.4% for BOD5, 39.97% for nitrates, 59.65% for ammoniacal nitrogen, and 48.06% for total nitrogen. Furthermore, the system exhibited a remarkable efficacy in eliminating pathogenic amoeba, achieving up to 70.42% removal, and coliforms, with a removal rate of 60%. However, an increase in parameters such as dissolved oxygen, electrical conductivity, total dissolved solids and phosphates was also observed. To achieve the required disinfection, tertiary treatments were evaluated: activated carbon filters, which achieved 62% removal of amoebas and 35% of coliforms, and a subsurface constructed wetland, which reached 100% elimination of amoebas and 40% of coliforms. These findings demonstrate that the thickness of the coconut fibre and the inclusion of worms directly influence the removal of contaminants and microorganisms. This positions the vermifilter as a promising solution for sanitation in rural areas. However, it is recommended to complement this system with disinfection or tertiary technologies to guarantee the quality of treated water. Keywords Amoeba; Bioremedation; Eisenia foetida; Vermifilter; Wastewater Treatment INTRODUCTION Water is one of the fundamental elements for life and development of society. However, population growth and the lack of adequate infrastructure have generated a global crisis related to access to clean water and safe sanitation (Gutiérrez et al., 2023; Chicaiza et al., 2020). According to global data, approximately 40% of the world's population lacks basic sanitation services, a problem that mainly affects rural areas and has serious implications for public health and the environment (Sagasta et al., 2015). In Ecuador, according to INEC (2022), more than 13% of the population lacks wastewater sanitation services, and in rural regions such as Baños of Cuenca, the situation is particularly alarming: only 59.18% of homes have sewerage and 29,79% directly discharge their wastewater into bodies of water, exacerbating contamination and health risks. Wastewater management is crucial to mitigating these issues, domestic wastewater contains solids, organic matter, nutrients, and microcontaminants, such as pathogens and emerging contaminants, which limit its safe use and discharge. While traditional treatments have proven effective, they are often expensive, require high levels of energy and resources, and are inaccessible to communities facing economic or geographic constraints. In this context, the need arises for sustainable and accessible alternatives, such as vermifiltration, a biological technology that employs earthworms and associated microorganisms to efficiently degrade organic matter and remove contaminants. Vermifiltration is a potentially promising and environmentally friendly solution for wastewater treatment in rural communities. In addition to its low operating and maintenance costs, this system uses living organisms to significantly reduce the physical, chemical and microbiological contaminants present in wastewater, helping to improve the quality of treated water and its potential reuse, for example, in agriculture. Recent studies highlight the efficiency of vermifilters in the elimination of pathogens such as coliforms and amoeba, which are key indicators of water quality (Parra 2023; Vintimilla, Zeas, 2024). This research focuses on evaluating the efficiency of a vermifilter installed in a house in Baños, Cuenca, for reducing contaminants present in domestic wastewater. This study aims not only to address the local problem, but also to provide a replicable model for other communities with similar conditions of lack of sanitation. The results of this project are expected to provide the implementation of sustainable solutions that improve the quality of life of families, protect ecosystems, and promote compliance with the sustainable development goals (Agenda 2030) related to water and sanitation. MATERIALS AND METHODS Study Area: The vermifilter is located in a single-family household without a wastewater treatment system, situated in the Unión Alta sector of the Baños, district of Cuenca, Ecuador. The area is at an altitude of 2,600 meters above sea level (m.s.n.m.), with an average temperature of 19°C (68°F) Preparation of the vermifilter: The filter is assembled in a high density polystyrene tank as showed in Figure 1 scheme. Figure 1. Vermifilter structure. Coconut fibre: Coconut fibre was used as a substrate layer due to its physical and chemical properties. They are optimal for the growth and reproduction of earthworms, due to its high porosity and good water retention capacity, as well as its resistance to decomposition, which allows the filter structure to be maintained for a longer period of time compared to other substrates (Curia et al. 2021). The worms take advantage of the lignin and cellulose present in the coconut fibre, which are rich sources of energy and favour their metabolism and reproduction. These characteristics improve treatment efficiency compared to more traditional substrates (Curia et al., 2021). We are working with two thicknesses of this layer, 15cm and 30cm, in order to test which one is more effective through laboratory analysis. Acclimatization of the earthworms. The earthworm used in this system was the Californian red worm (Eisenia foetida). Approximately 5,000 specimens were obtained from the Santa Ana parish in the city of Cuenca, with individual weights ranging from 250 and 400 g. The worms were mixed with compost to create optimal conditions for their adaptation and better acclimatization. To avoid damaging the earthworm’s dermis, they were fed a mixture of manure and wastewater during the first fifteen days. Gradually, more wastewater was feed into the vermifilter. The acclimatization process lasted six weeks, and to ensure the survival of the worms, a control of pH (6.5 - 7.5), humidity (70 - 80 %) and temperature (15 - 25 °C) was carried out. Laboratory Analysis. Three scenarios are proposed to determine the pollutants removal capacity of the vermifilter: a filter without earthworms (control), a vermifilter with 15 cm of coconut fibre, and a vermifilter with 30 cm of coconut fibre. Monitoring points: Vermifilter inlet, Vermifilter outlet (with its three variants: without worms, 15cm and 30cm of coconut fiber thickness). In situ physical analysis, temperature, dissolved oxygen, total dissolved solids, electrical conductivity and pH were carried out with the HACH multiprobe HQ40d portable equipment. Chemical analysis: carried out in the Water Quality Laboratory of the Faculty of Chemical Sciences of the University of Cuenca, the main parameters analyzed were: Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), phosphates, nitrates, ammonia nitrogen and solids: total, suspended and volatile. Microbiological analyses: total and fecal coliforms were monitored using lauryl sulphate broth as culture medium and amoeba using the culture medium established by Moreno L. (2018) (Page solution and agar) for the seeding of amoeba, following the methodology described by Hernández et al. (2022). Tertiary treatment, with the purpose of seeking alternatives to eliminate amoebae and coliforms, two tertiary treatments were proposed: mineral and vegetable activated carbon filters (at laboratory scale) and connection to a subsurface artificial wetland. RESULTS AND DISCUSSION The reduction of contaminants with vermifilter treatment (VF) has been generally attributed to the joint action of earthworms and microorganisms present in the system. One of the main reasons for a significant reduction of COD showed in the results could be the metabolism of aerobic and anaerobic macro and micro heterotrophic organisms which through organic compounds in the water, produce biomass and chemical reactions of oxide reduction, favoring the process (Castillo and Chimbo ,2021). Results showed that VF 30 resulted more efficient removing COD, BOD and nitrates (Figure 2). Figure 2. BOD, COD and nitrate removal rates. In contrast, an increase in the concentration of TDS, DO and phosphates were detected after VF treatment (Figure 3). With regards to phosphorus, there was an increase after the VF 30cm treatment, which can be attributed to the fact that the earthworms had a better stabilization and a more favourable habitat, which increases the mineralization of organic matter and, therefore, the release of nutrients such as phosphates. In addition, the greater depth provides a more stable and less disturbed environment, favouring more efficient biogeochemical processes that result in higher phosphate concentrations in the effluent (Naranjo & Quezada, 2024). However, the amount of phosphorus is within the ranges allowed by the regulations for discharge to fresh water and can be a plus for the reuse of water for irrigation of tree crops, since it has phosphates that enrich the soil. Figure 3. Increase of TDS, DO and Phosphates. Figures 4 and 5 show the removal percentage of amoeba and total coliforms, which after a stabilization process tended to remain stable. The fact that removal was more efficient with VF30 than with VF15 may be attributed to the fact that substrate thickness affects removal efficiency, finding that a deeper substrate can significantly improve the treatment capacity of the system. A thicker substrate allows the water to remain longer in contact with the microorganisms and worms, promoting the growth of a more stable and active microbial community, which contributes to more efficient degradation of contaminants (Dey Chowdhury & Bhunia, 2021). Figure 4. Amoeba removal Figure 5. Total coliforms removal This study also included two trials to evaluate microbiological disinfection after vermifiltration. In the first, activated carbon filters, both mineral and vegetable, were used (elimination of 62% amoebae and 30% coliforms), while in the second, a subsurface artificial wetland was implemented (elimination of 100% amoebae and 40% coliforms). Then, we can conclude that the treated water after vermifiltration followed disinfection is suitable for irrigation of crops and ornamental plants, where the microbiological risk is lower. This represents a promising approach to water sustainability in rural areas, promoting the circular economy by reincorporating treated water into agricultural systems. However, their use in more stringent applications, such as food crops or reuse in closed systems, will require additional research to completely eliminate pathogens. This study underscores the importance of developing technologies that are accessible and adapted to local conditions, driving sustainable practices in the management of treated water. REFERENCES Castillo, J., Chimbo, J. (2021) Eficiencia en la remoción de materia orgánica mediante lombrifiltros (Eisenia foetida) en aguas residuales domésticas para zonas rurales. https://doi.org/10.29019/enfoqueute.746 Chicaiza, C., Huaraca, L., Almeida-Naranjo, C. E., Guerrero, V. H., & Villamar, C. A. (2020). Improvement of organic matter and nutrient removal from domestic wastewater by using intermittent hydraulic rates on earthworm–microorganism biofilters. 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