Effect of hydraulic loading rate and pollutants degradation kinetics in two stage hybrid macrophyte assisted vermifiltration system

A multi-criteria approach to test and evaluate the efficiency of two composting systems under two different climates

The selection of the appropriate composting system, climate conditions, and duration of the composting process are important parameters for municipal solid waste composting. Therefore, this research aimed to design, test, and evaluate two different static composting systems under two different climate regions, Palestine and India, following a multi-criteria approach. A forced-aeration composting system was designed for use in Palestine, and a naturally aerated one was used in India. Three experiments were conducted, two of them in Palestine and one in India. The operational parameters were controlled and monitored during the composting process, while the physio-chemical and biological parameters were tested to evaluate the compost end quality. The results showed that both systems provide good efficiency toward formation of final compost (39-43 days in Palestine, and 31 days in India), and the average materials' volume reduction was almost 60%. The physio-chemical analysis showed that most of the parameters comply with the threshold limits specified by the Palestinian Standards Institution (PSI) and Indian Fertilizer Control Order (FCO) except for minor deviations. Both systems provided a high fertility index (4.3, 4.7, and 4.8), and a high clean index (4.6, 5.0, and 4.7). However, the results of the biological parameters showed that all the experiments met PSI, but none of them met FCO, suggesting that the outer edges of the composting system didn't heat enough to inactivate pathogenic microbes, therefore, developing the system by adding turning option could overcome this shortcoming. It was concluded that the forced aeration system is suitable for Palestine, while the natural aeration system is suitable for India.Implications: Municipal solid waste management is facing technical and financial challenges worldwide due to the increasing generation of solid waste following the population growth. The current improper management of this waste stream through landfilling is adding pressure on the environment as a result of methane emissions and landfill leachate. Therefore, composting of the organic fraction through selection of an appropriate composting system can solve many waste management problems and contribute to environmental sustainability. This research focuses on design, test and evaluate two composting systems in two regions with different climatic conditions, Palestine and India as both are facing waste management problems. The outcome of this research optimized the composting process which can be replicated and scaled up in other countries worldwide with similar climatic conditions.

New developments on vermifiltration as a bio-ecological wastewater treatment technology: Mechanism, application, performance, modelling, optimization, and sustainability

The review discusses the advancements in vermifiltration research over the last decade, focusing on pollution removal mechanisms, system performance, the fate of filter components, and by-products. Vermifiltration has demonstrated remarkable capabilities, particularly in treating highly contaminated wastewater with Chemical Oxygen Demand (COD) levels exceeding 92,000 mg/L and Biochemical Oxygen Demand (BOD5) levels over 25,000 mg/L, achieving removal rates of approximately 89% and 91%, respectively. Importantly, vermifiltration maintains its effectiveness even with fluctuating organic loads at the inlet, thanks to optimization of parameters like Hydraulic Loading Rate, biodegradable organic strength, earthworm density and active layer depth. Clogging issues can be minimized through parameters optimization. The review also highlights vermifiltrations' potential in co-treating the organic fraction of municipal solid waste while significantly reducing heavy metal concentrations, including Cd, Ni, Pb, Cu, Cr, and Zn, during the treatment process. Earthworms play a pivotal role in the removal of various components, with impressive removal percentages, such as 75% for Total Organic Carbon (TOC), 86% for Total COD, 87% for BOD5, 59% for ammonia nitrogen, and 99.9% for coliforms. Furthermore, vermifiltration-treated effluents can be readily utilized in agriculture, with the added benefit of producing vermicompost, a nutrient-rich biofertilizer. The technology contributes to environmental sustainability, as it helps reduce greenhouse gas emissions (GHG), thanks to earthworm activity creating an aerobic environment, minimizing GHG production compared to other wastewater treatment methods. In terms of pollutant degradation modeling, the Stover-Kincannon model outperforms the first-order and Grau second-order models, with higher regression coefficients (R2 = 0.9961 for COD and R2 = 0.9353 for TN). Overall, vermifiltration emerges as an effective and sustainable wastewater treatment solution, capable of handling challenging wastewater sources, while also producing valuable by-products and minimizing environmental impacts.

Effects of bed depths and the ratio of aerobic to anaerobic zone on the performance of horizontal subsurface flow macrophyte-assisted high-rate vermifilters treating synthetic brewery wastewater

Effects of total vermibed depth, as well as the ratio of aerobic (the unsubmerged) to anaerobic (the submerged) zone on the performance of the horizontal subsurface flow macrophyte-assisted vermifilters (HSSF-MAVFs) treating synthetic brewery wastewater at a higher hydraulic loading rate (HLR), were investigated for the first time. Results showed that the HSSF-MAVF with a 50 cm total and 18 cm submerged vermibed depth yielded the optimum removal of the pollutants, ensuring a (91.2 ± 1.7)%, (81.8 ± 1.9)%, (67.4 ± 3.9)%, and (63.1 ± 2.3)% removal of chemical oxygen demand (COD), ammonium N (NH4 + -N), total N (TN), and organic N, respectively, whereas there was an increase of (142 ± 6.3)% in the effluent nitrate-N (NO3 - -N) than that in the influent. At the optimum condition, the effluent concentrations of all the pollutants including COD, NH4 + -N, NO3 - -N, TN, and organic N were well below the surface water discharge standards specified by the Central Pollution Control Board (CPCB), and thus, the effluent of the HSSF-MAVF could be safely discharged into the surface water bodies. PRACTITIONER POINTS: Total vermibed depth of HSSF-MAVFs was optimized for organic and nitrogen removal. HSSF-MAVFs were subjected to the higher HLR of synthetic brewery wastewater. Removal of COD and NH4 + -N was decreased with the increase in submerged bed depth. Removal of organic N and TN was increased with the increase in submerged bed depth. Total/unsubmerged bed depth had a positive impact on the organic and N removal.

Vermifiltration: Strategies and techniques to enhance the organic and nutrient removal performance from wastewater

The vermifiltration (VF) technology has gained significant attention as a green alternative for remediating domestic and industrial wastewater over the last few decades. Of late, the implementation of various modifications to the orthodox VF technology, including tweaks in the design and operation of the vermifilters, has been portrayed in the available literature. However, owing to the scatteredness of the available information, the knowledge regarding the execution of the modified vermifilters is still inadequate. Hence, an effort has been made to comprehensively overview the innovative strategies and techniques adopted to improve the organic and nutrient removal potential of the VFs from wastewater. In addition, future perspectives have been recognized to design more efficient and sustainable VFs. This review explores more of such novel tactics to improve the performance of the VF technology regarding organic and nutrient removal from wastewater. PRACTITIONER POINTS: Innovative strategies and techniques implemented to VF technology were comprehensively overviewed. Design modification and advantages of each innovation were highlighted. The pollutant removal performance of every modification was emphasized. Modified vermifilters were better than the conventional vermifilters in terms of organic and nutrient removal from the wastewater.

Reduction performance of microplastics and their behavior in a vermi-wetland during the recycling of excess sludge: A quantitative assessment for fluorescent polymethyl methacrylate

Large amounts of microplastics (MPs) that have accumulated in excess sludge may increase the environmental risk for its subsequent treatment. This study aimed to investigate the performance and mechanism of the reduction of MPs in excess sludge in a vermi-wetland. For this, 1 μm, 100 μm, and 500 μm of fluorescent MPs stained with Nile red were added to raw sludge, and their decreased numbers were quantified during the treatment of sludge. The results showed that the removal rates of chemical oxygen demand and total solids from the excess sludge were 63.44%-90.98% and 37.61%-51.56% in the vermi-wetland, respectively. The numbers of 1 μm, 100 μm, and 500 μm MPs could be reduced by 86.62%-95.69%, 95.44%-99.52%, and 100% in the vermi-wetland, respectively. These results indicate that the vermi-wetland is more effective at eliminating MPs. Further insight into the vermi-wetland stratification was obtained, and more than 74.87% of the MPs were intercepted in the vermicompost layer. Moreover, all the particle sizes of MPs were found in the excrement of earthworms. However, only 1 μm MPs were detected in their digestive organs. This study suggests that the interception effect is primarily responsible for elimination of MPs in excess sludge, and the bioturbation of earthworms plays an important role in the mobilization of MPs in vermi-wetlands.

Performance and stratified microbial community of vermi-filter affected by Acorus calamus and Epipremnum aureum during recycling of concentrated excess sludge

Vermi-filter combined with wetland plant (VFP) is an eco-friendly and sustainable approach for recycling of excess sludge by joint action of earthworms, wetland plants and microorganisms. However, the effects of wetland plants on sludge decomposition and involved microorganisms are remain unclear. This study investigated the effects of wetland plants on the treatment performance of VFP for concentrated excess sludge and microbial community distribution inside the VFP. The wetland plants' species of Acorus calamus and Epipremnum aureum were separately planted on the surface layer of vermi-reactors by earthworms Eisenia fetida. Results showed that the growth rate of E. fetida in VFPs significantly (P < 0.001) increased by 75%, compared to VF. In addition, the removal rates of total solids and chemical oxygen demand in VFPs could reach 61%-79% and 36%-68%, respectively, displaying a better performance of sludge reduction than in the VF. The surface layer of VFPs was a hotspot for degradation of organic matter, where bacteria played an important role in bio-decomposition rather than eukaryotes. Moreover, wetland plants could significantly (P < 0.001) enrich the eukaryotic population, rather than bacterial population. Compared to the VF, the wetland plants could promote the diversities of bacterial community in VFPs, showing specific functioned genus in different layers. In contrast, A. calamus could be a better candidate than E. aureum in the VFP. This study suggests that the inoculation of wetland plants can improve the performance for treating concentrated excess sludge by changing the biomass of earthworms and the structure of microbial community within the VFP.

Nitrogen removal in vermifiltration: Mechanisms, influencing factors, and future research needs

To meet global health and sanitation goals, there is a continued need for sustainable wastewater treatment alternatives that require minimal energy and investment. Vermifiltration, a technology gaining relevance in Africa and Asia, may be an alternative to traditional wastewater treatment systems due to its cost-effectiveness, ease of application and maintenance, and sustainability. However, nitrogen removal in vermifiltration is not well understood since most of the prior research focuses on organics removal. Thus, a state of the art review is necessary to separately focus on the mechanisms associated with nitrogen removal in vermifiltration, along with the factors affecting nitrogen removal. For the first time, this review attempts to present the types of vermifilter based on their flow pattern. The review further discusses the current status of the application of vermifiltration, along with the benefits and limitations associated with the adoption of this technology. It also explores possible strategies that could be adopted to maximize the nitrogen removal potential of vermifilters as optimizing nitrogen removal is critical for improving the performance of vermifiltration based treatment systems.

Kinetic and Prediction Modeling Studies of Organic Pollutants Removal from Municipal Wastewater using Moringa oleifera Biomass as a Coagulant

This study investigated the potential of Moringa oleifera (MO) seed biomass as a coagulant for the removal of turbidity, biochemical oxygen demand (BOD), and chemical oxygen demand (COD) of municipal wastewater. Triplicated laboratory experiments using MO coagulant added at varying treatment dosages of 50, 100, 150, 200 mg/L, and a control (0 mg/L) treatment were performed for a settling period of 250 min at room temperature. Kinetics and prediction variables of cumulative turbidity, BOD, and COD removal were estimated using simplified first order and modified Gompertz models. Results showed that the maximum removal of turbidity, BOD, and COD were 94.44%, 68.72%, and 57.61%, respectively, using an MO dose of 150 mg/L. Various kinetic parameters, such as rate constant (r), measured (REm) versus predicted (REp) cumulative removal, and specific pollutant removal rate (µm), were also maximum when an MO dose of 150 mg/L was added, the standard error being below 5%. The developed models were successfully validated over multiple observations. This study suggests low cost and sustainable removal of turbidity, BOD, and COD of municipal wastewater using MO seed biomass as a coagulant.

Improvement of organic matter and nutrient removal from domestic wastewater by using intermittent hydraulic rates on earthworm-microorganism biofilters

Biofilters based on earthworms-microorganisms represent, particularly in developing countries, an interesting alternative for domestic wastewater treatment due to their easy operation and low cost. However, there are several operational aspects that should be better understood in order to improve their performance. This paper studies the effect of using intermittent hydraulic loading rates to improve organic matter and nutrient removal from domestic wastewater using these biofilters. Three laboratory-scale columns, operating at a 2.5 m³ m^-2day^-1 hydraulic loading rate, were used. The B_{1-24 h}, B_{2-8 h}, B_{3-4 h} column loading rates indicate that the columns were operated continuously for 24, 8 and 4 h, respectively. Each column (biomass biofilm/earthworms, redox potential, and head loss) and its corresponding operational performance parameters (TCOD, NH₄ ⁺, NO₃ ^-, NO₂ ^-, TP) were monitored. The results showed that the B_{2-8 h} intermittent hydraulic loading rate results in the best global performance, with 74%, 57%, and 20% average removal efficiencies for TCOD, nitrogen, and phosphorus, respectively. Moreover, it showed the best biomass growth (biofilm and earthworms), activity (as redox potential changes) and the lowest clogging effects (up to -1.0 cm). The intermittent operation influences the behavior of the earthworm-microorganism biofilters and offers the possibility of optimizing its global performance and achieving a resilient technology.

Are vegetated drainage ditches effective for nitrogen removal under cold temperatures?

Vegetated ditches are widely used to treat agricultural wastewater, but effective nitrogen removal at low temperatures remains a challenge because plants wilt in the winter. In this study, three simulated drainage ditches vegetated with Myriophyllum aquaticum were operated with low, medium, and high water levels to study ammonium nitrogen (NH₄⁺-N) removal under cold temperatures. The M. aquaticum ditches had a mean NH₄⁺-N removal efficiency of 75.8-86.8% throughout cold period. Based on nitrogen mass balance, plant uptake, sediment adsorption, and microbial removal accounted for 12.4-21.5%, 0.0-8.1%, and 38.9-54.6% of the influent total nitrogen loading, respectively. The accumulation of nitrate confirmed that intense microbial nitrification occurred in M. aquaticum ditches even at low temperature. These results suggest that M. aquaticum is appropriate as a cold-tolerant plant for NH₄⁺-N removal in drainage ditches.

Vermifiltration as a sustainable natural treatment technology for the treatment and reuse of wastewater: A review

With increasing urbanization and industrialization, the scarcity of freshwater is becoming rampant. To counteract this, authorities all over the world are forced to consider the treatment and reuse of the wastewater produced by either industries or domestic units. After an extensive literature survey, vermifiltration coupled with/without macrophyte has been identified as one of the best sustainable, natural and eco-friendly technology for the treatment and reuse of wastewater. Till date, it has been successfully applied for treating domestic wastewater. However, the results from very limited industrial applications are also encouraging and proving its worth for industrial wastewater remediation. The present review on vermifiltration deals with the mechanisms involved and its current status for the remediation and reutilisation of the effluents generated from domestic and industrial premises. The review successfully identifies and explicitly discusses the mechanisms involved in the vermifiltration. The review exhaustively discusses the performance of vermifiltration and identifies the factors contributing to the performance of vermifiltration, which could be of help in designing of the field scale vermifilter based treatment plant. The review identifies the limitations associated with the vermifiltration and suggests possible alternatives, aimed to improve its performance and applicability. The aim of this review is to bring the attention of prospective researchers to study each and every aspect related to the vermifiltration so that it may be adopted as a reliable and dependable technology for the remediation of several industrial effluents meeting the concept of "Zero discharge".

Fate of filter materials and microbial communities during vermifiltration process

The fate of filter materials and microbial communities during the vermifiltration process were studied for 5 months while treating the concentrated greywater. Four filters were filled with 10 cm gravel of which a layer of medium size gravel (5 cm thickness, aggregate size 20-40 mm) at the bottom and a layer of coarse gravel (5 cm thickness, aggregate size 10-20 mm) at the top, then filled with 20 cm sand (d₆₀ = 0.2 mm, d₁₀ = 0.118 mm). Finally, Vermifilter 1 (VF1), control unit and Vermifilter 2 (VF2), were filled with 40 cm fine sawdust (0.05-5 mm) but Vermifilter 3 (VF3), was filled with 40 cm cow dung (0.05-5 mm). Three filters were inoculated with 200 individuals of Eudrilus eugeniae except for the control unit which was filled with sawdust. Five sampling ports were installed on the wall of the filters at 10 cm intervals with reference to the surface of the top layer. Three of the filters were supplied with concentrated greywater and VF1 was supplied with drinking water at the hydraulic loading rate of 16 L m^-2.d^-1 on batch basis, i.e., four times a day at 8:00 a.m., 11:00 a.m., 2:00 p.m. and 5:00 p.m. Weekly, samples from influent and effluent, and monthly, samples of filter materials collected via sampling ports, were collected and analyzed.The removal efficiencies of biological oxygen demand (BOD₅), total chemical oxygen demand (tCOD), and dissolved chemical oxygen demand (dCOD) of VF2 and VF3 were 5-7% higher than the control unit, but little differences were observed in terms of total suspended solids (TSS). However, the removal efficiencies of nutrients for the control unit was slightly better than VF2 and VF3. The pH and Moisture content (MC) of filter materials increased along the depth, but percentage of volatile solids to total solids (VS/TS) decreased through time due to the high number of microbial communities and earthworms dominating the top layer compared to the bottom. The performance of VF2-sawdust was slightly better than VF3-cow dung to treat concentrated greywater.

Design and development of a hybrid macrophyte assisted vermifilter for the treatment of dairy wastewater: A statistical and kinetic modelling approach

Global urbanization, exponential increase in population and sophisticated life style of the present generation are the major causes leading to a rapid increase in water demand in recent years. In order to nullify this rising water demand, it's high time to reuse domestic as well as industrial effluent after providing suitable chemical/biological treatment. Macrophyte filter incorporated with earthworm is identified as one of the most economic system for the treatment purpose in developing countries. However, very few literatures and technical information are available to scale up the design and its easy operation. This paper aims to develop a hybrid system and assess its performance for the purification of dairy wastewater. In the present study, two stage macrophyte assisted vermifilters (MAVFs) have been designed. The 1st stage encompassed a vertical flow (VF) unit, and the 2nd stage contained a horizontal flow (HF) unit. Both the units were inoculated with earthworm Eisenia fetida and were planted with Canna indica. Box-Behnken model was applied to design the system and study the effect of various parameters. It was observed that hybrid MAVF system removed a maximum of 83.2% COD and 57.3% TN at HLR 0.6 m/d and an active layer depth of 30 cm. Ammonification and nitrification typically occurred in the active layer (earthworm inoculated zone) of VF unit due to high activity of earthworms and its associated gut microbes, whereas HF unit facilitate denitrification process. Earthworm growth characteristics in the system were monitored, which is an imperative factor for the design of MAVF reactor. Kinetic modelling of 1st order, grau 2nd order and Stover-Kincannon model were performed and the Stover-Kincannon model showed high regression coefficient (COD, R² 0.9961 and TN, R² 0.9353) supporting its applicability as compared to the other models.

Study on the biomass and size spectra of bio-particles in vermifilter biofilms

In biological processes of sludge treatment, the sludge yield is closely related to the energy dissipation of entire microbial system. The vermifilter (VF), a novel biofilter, works efficiently due to the introduction of earthworms, which modifies the energy flow pathway through the variations of microbial size structure. For a deep insight into the sludge reduction in the VF, the biomass size spectrum (BSS) was employed to map the energy dissipation in the VF. The results indicated that bio-particles in the size class of [31, 63] μm were reduced most in the excess sludge after the VF treatment. In biofilms, bio-particles in the size class of [31, 63] μm varied most with the filter depth and earthworm density. Eight biomass and size spectra (BSS) were established for all beds of the VF and BF (the control of the VF, without earthworms). The normalized BSS were all linear both in the VF and BF, and their linear regression parameters, the slopes (k) and intercepts (b), varied with the filter depth and the earthworm density. The k and b of the VF were both significantly different from those of the BF. According to the k, the productivity level of largest bio-particles was higher in the VF than in the BF. According to the b, bio-particles at the bottom of size structure could be taken faster in the VF than in the BF. At last, some improvement approaches with some tries were proposed to enhance the sludge treatment capacity of the VF.