Post-treatment and agricultural reuse of digestate from low-tech digesters: A comparative life cycle assessment.

The objective of this study was to analyse the environmental impacts of the post-treatment and agricultural reuse of digestate from a low-tech digester implemented in a small-scale farm in Colombia using the Life Cycle Assessment methodology. The scenarios considered were: 1) digestate post-treatment with a sand filter and its reuse in agriculture; 2) digestate post-treatment with a vermifilter and the production of compost, and 3) untreated digestate directly applied on the agricultural land (current scenario). Moreover, an economic analysis was also addressed. Results showed that the vermifilter was the most environmentally friendly scenario. It considerably reduced (by up to 9 times) the environmental impacts compared to the other scenarios. From an economic point of view, the implementation of the vermifilter generated an increase in farmers' income (up to 70 $ year-1) since it avoids buying synthetic fertilizer. Finally, the implementation of a vermifilter for the post-treatment and agricultural reuse of digestate from low-tech digesters showed to have both environmental and economic benefits. This technology can help to promote the circular bioeconomy in small-scale farms, reducing poverty and improving the standard of living in rural areas.

Constructed wetlands for winery wastewater treatment: A review on the technical, environmental and socio-economic benefits.

In wineries, wastewater production and solid waste generation can pose serious environmental threats. Winery wastewater production has a seasonal behavior and needs a treatment system that can adapt to these fluctuations while reducing costs, and environmental impacts and promoting other winery activities. The implementation of constructed wetlands (CWs) has been demonstrated to be a competitive solution for winery wastewater and sludge treatment. In this article, worldwide experiences over the last 25 years of CWs for winery wastewater treatment are reviewed. The review shows that the application of hybrid CWs coupled with anaerobic digestion can reduce >90 % of the organic pollutants and solids from winery wastewater while avoiding clogging. These efficiencies and advantages can be also attained with French vertical systems. Not only CWs have a good technical performance, but they also reduce up to >90 % the environmental impacts associated with winery wastewater treatment. It is due to low energy requirements, no chemicals consumption and avoidance of off-site management and transportation practices. In terms of costs, CWs can reduce up to 60 times the costs associated with winery wastewater treatment and management. More efforts should be made in order to define the social benefits of this technology and the quality of the recovered resources (e.g. treated water, fertilizer) in order to promote the circular economy without compromising human and ecosystem health.

Nature-based solutions for wastewater treatment and bioenergy recovery: A comparative Life Cycle Assessment.

The aim of this study was to assess the environmental impacts of up-flow anaerobic sludge blanket (UASB) reactors coupled with high rate algal ponds (HRAPs) for wastewater treatment and bioenergy recovery using the Life Cycle Assessment (LCA) methodology. This solution was compared with the UASB reactor coupled with other consolidated technologies in rural areas of Brazil, such as trickling filters, polishing ponds and constructed wetlands. To this end, full-scale systems were designed based on experimental data obtained from pilot/demonstrative scale systems. The functional unit was 1 m3 of water. System boundaries comprised input and output flows of material and energy resources for system construction and operation. The LCA was performed with the software SimaPro®, using the ReCiPe midpoint method. The results showed that the HRAPs scenario was the most environmentally friendly alternative in 4 out of 8 impact categories (i.e. Global warming, Stratospheric Ozone Depletion, Terrestrial Ecotoxicity and Fossil resource scarcity). This was associated with the increase in biogas production by the co-digestion of microalgae and raw wastewater, leading to higher electricity and heat recovery. From an economic point of view, despite the HRAPs showed a higher capital cost, the operation and maintenance costs were completely offset by the revenue obtained from the electricity generated. Overall, the UASB reactor coupled with HRAPS showed to be a feasible nature-based solution to be used in small communities in Brazil, especially when microalgae biomass is valorised and used to increase biogas productivity.

Life cycle assessment of microalgae systems for wastewater treatment and bioproducts recovery: Natural pigments, biofertilizer and biogas.

The aim of this study was to assess the potential environmental impacts associated with microalgae systems for wastewater treatment and bioproducts recovery. In this sense, a Life Cycle Assessment was carried out evaluating two systems treating i) urban wastewater and ii) industrial wastewater (from a food industry), with the recovery of bioproducts (i.e. natural pigments and biofertilizer) and bioenergy (i.e. biogas). Additionally, both alternatives were compared to iii) a conventional system using a standard growth medium for microalgae cultivation in order to show the potential benefits of using wastewater compared to typical cultivation approaches. The results indicated that the system treating industrial wastewater with unialgal culture had lower environmental impacts than the system treating urban wastewater with mixed cultures. Bioproducts recovery from microalgae wastewater treatment systems can reduce the environmental impacts up to 5 times compared to a conventional system using a standard growth medium. This was mainly due to the lower chemicals consumption for microalgae cultivation. Food-industry effluent showed to be the most promising scenario for bioproducts recovery from microalgae treating wastewater, because of its better quality compared to urban wastewater which also allows the cultivation of a single microalgae species. In conclusion, microalgae wastewater treatment systems are a promising solution not only for wastewater treatment but also to boost the circular bioeconomy in the water sector through microalgae-based product recovery.

Benefits and risks of agricultural reuse of digestates from plastic tubular digesters in Colombia.

The aim of this study is to characterize the digestates from three plastic tubular digesters implemented in Colombia fed with: i) cattle manure; ii) cattle manure mixed with cheese whey; iii) pig manure. All the digesters worked under psychrophilic conditions. Physico-chemical characteristics, heavy metals, pathogens, and agronomic quality were investigated. All the digestates were characterized by physico-chemical characteristics and nutrients concentration suitable for their reuse as biofertilizer. However, these digestates may only partially replace a mineral fertilizer due to the high nutrients dilution. Heavy metals were under the detection limit of the analytical method (Pb, Hg, Ni, Mo, Cd, Chromium VI) or present at low concentration (Cu, Zn, As, Se) in all the digestates. Biodegradable organic matter and pathogens (coliform, helminths and Salmonella spp.) analysis proved that all the digestates should be post-treated before soil application in order to prevent environmental and health risks, and also to reduce residual phytotoxicity effects. The digestate from pig manure had a higher nutrient percentage (0.2, 0.6 and 0.05 % w/w of total N, P2O5 and K2O, respectively), but also higher residual phytotoxicity than the other digestates. Co-digestion seemed not to significantly improve the digestate fertilizing potential. Finally, further studies should address how to improve fertilizing potential of digestates from plastic tubular digesters, avoiding environmental and health risks.

Health and environmental impacts of drinking water choices in Barcelona, Spain: A modelling study.

Quantitative evidence of health and environmental tradeoffs between individuals' drinking water choices is needed to inform decision-making. We evaluated health and environmental impacts of drinking water choices using health impact and life cycle assessment (HIA, LCA) methodologies applied to data from Barcelona, Spain. We estimated the health and environmental impacts of four drinking water scenarios for the Barcelona population: 1) currently observed drinking water sources; a complete shift to 2) tap water; 3) bottled water; or 4) filtered tap water. We estimated the local bladder cancer incidence attributable to trihalomethane (THM) exposure, based on survey data on drinking water sources, THM levels, published exposure-response functions, and disability-adjusted life years (DALYs) from the Global Burden of Disease 2017. We estimated the environmental impacts (species lost/year, and resources use) from waste generation and disposal, use of electricity, chemicals, and plastic to produce tap or bottled drinking water using LCA. The scenario where the entire population consumed tap water yielded the lowest environmental impact on ecosystems and resources, while the scenario where the entire population drank bottled water yielded the highest impacts (1400 and 3500 times higher for species lost and resource use, respectively). Meeting drinking water needs using bottled or filtered tap water led to the lowest bladder cancer DALYs (respectively, 140 and 9 times lower than using tap water) in the Barcelona population. Our study provides the first attempt to integrate HIA and LCA to compare health and environmental impacts of individual water consumption choices. Our results suggest that the sustainability gain from consuming water from public supply relative to bottled water may exceed the reduced risk of bladder cancer due to THM exposure from consuming bottled water in Barcelona. Our analysis highlights several critical data gaps and methodological challenges in quantifying integrated health and environmental impacts of drinking water choices.

Promotion of full-scale constructed wetlands in the wine sector: Comparison of greenhouse gas emissions with activated sludge systems.

The aim of this study was to quantify and compare greenhouse gas (GHG) (i.e. carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4)) emissions from two full-scale winery wastewater and sludge treatment systems (i.e. constructed wetlands (CWs) and activated sludge system) located in Galicia (Spain). GHG fluxes were measured using the static chamber method in combination with an on-site Fourier transform infrared spectroscopy (FTIR) gas analyser in the CWs system. These on-site innovative techniques proved to be very accurate and reliable. In the activated sludge treatment systems, the floating chamber method in combination with the FTIR gas analyser was used. Measurements were carried out during the vintage season, when winery wastewater has the highest flow and loads, and the rest of the year. Emission rates of CO2, N2O and CH4 in the CWs units (i.e. vertical flow, horizontal subsurface flow and sludge treatment wetlands) ranged from 1.35E+02 to 7.54E+04, 1.70E-01 to 3.09E+01 and - 3.05E+01 to 1.79E+03 mg m-2 day-1, respectively. In the case of the activated sludge units (i.e. reactor, secondary settler and sludge storage tank) emission rates of CO2, N2O and CH4 ranged from 1.56E+04 to 1.43E+05, 1.13E+01 to 4.75E+01 and 2.52E+01 to 1.01E+03 mg m-2 day-1, respectively. Seasonally, daily and instantaneous variability in emissions as well as spatial variability was found. Comparing CWs with the activated sludge system, surface emission rates were lower in the CWs system in both seasons considered. Results highlighted that CWs are suitable technologies that can help to reduce GHG emissions associated with winery wastewater treatment.

Low-cost anaerobic digester to promote the circular bioeconomy in the non-centrifugal cane sugar sector: A life cycle assessment.

This study aimed to assess the potential environmental benefits of implementing low-cost digesters to valorize agro-industrial waste in the non-centrifugal cane sugar (NCS) sector. Two scenarios were considered: i) the current scenario in which organic waste and wastewater were burned outdoor and discharged into a water body, respectively; ii) the anaerobic digestion (AD) scenario, in which low-cost biodigesters were used for organic waste and wastewater treatment on-site. Results showed that low-cost digesters were a sustainable alternative to mitigate environmental impacts, especially those associated with water source pollution. Indeed, in the AD scenario, the environmental impact categories of Freshwater Eutrophication and Marine Eutrophication showed a decrease of 87.6% and 99.4%, respectively, compared to the current scenario. Thus, by treating organic waste and wastewater on-site while producing bioproducts (i.e. biofuel and biofertilizer), low-cost digesters could contribute to boosting the circular bioeconomy in the NCS production sector.

Constructed wetlands operated as bioelectrochemical systems for the removal of organic micropollutants.

The removal of organic micropollutants (OMPs) has been investigated in constructed wetlands (CWs) operated as bioelectrochemical systems (BES). The operation of CWs as BES (CW-BES), either in the form of microbial fuel cells (MFC) or microbial electrolysis cells (MEC), has only been investigated in recent years. The presented experiment used CW meso-scale systems applying a realistic horizontal flow regime and continuous feeding of real urban wastewater spiked with four OMPs (pharmaceuticals), namely carbamazepine (CBZ), diclofenac (DCF), ibuprofen (IBU) and naproxen (NPX). The study evaluated the removal efficiency of conventional CW systems (CW-control) as well as CW systems operated as closed-circuit MFCs (CW-MFCs) and MECs (CW-MECs). Although a few positive trends were identified for the CW-BES compared to the CW-control (higher average CBZ, DCF and NPX removal by 10-17% in CW-MEC and 5% in CW-MFC), these proved to be not statistically significantly different. Mesoscale experiments with real wastewater could thus not confirm earlier positive effects of CW-BES found under strictly controlled laboratory conditions with synthetic wastewaters.

Natural Pigments and Biogas Recovery from Microalgae Grown in Wastewater.

This study assessed the recovery of natural pigments (phycobiliproteins) and bioenergy (biogas) from microalgae grown in wastewater. A consortium of microalgae, mainly composed by Nostoc, Phormidium, and Geitlerinema, known to have high phycobiliproteins content, was grown in photobioreactors. The growth medium was composed by secondary effluent from a high rate algal pond (HRAP) along with the anaerobic digestion centrate, which aimed to enhance the N/P ratio, given the lack of nutrients in the secondary effluent. Additionally, the centrate is still a challenging anaerobic digestion residue since the high nitrogen concentrations have to be removed before disposal. Removal efficiencies up to 52% of COD, 86% of NH4 +-N, and 100% of phosphorus were observed. The biomass composition was monitored over the experimental period in order to ensure stable cyanobacterial dominance in the mixed culture. Phycocyanin and phycoerythrin were extracted from harvested biomass, achieving maximum concentrations of 20.1 and 8.1 mg/g dry weight, respectively. The residual biomass from phycobiliproteins extraction was then used to produce biogas, with final methane yields ranging from 159 to 199 mL CH4/g VS. According to the results, by combining the extraction of pigments and the production of biogas from residual biomass, we would not only obtain high-value compounds, but also more energy (around 5-10% higher), as compared to the single recovery of biogas. The proposed process poses an example of resource recovery from biomass grown in wastewater, moving toward a circular bioeconomy.

Fate of priority pharmaceuticals and their main metabolites and transformation products in microalgae-based wastewater treatment systems.

The present study evaluates the removal capacity of two high rate algae ponds (HRAPs) to eliminate 12 pharmaceuticals (PhACs) and 26 of their corresponding main metabolites and transformation products. The efficiency of these ponds, operating with and without primary treatment, was compared in order to study their capacity under the best performance conditions (highest solar irradiance). Concentrations of all the target compounds were determined in both water and biomass samples. Removal rates ranged from moderate (40-60 %) to high (>60 %) for most of them, with the exception of the psychiatric drugs carbamazepine, the ß-blocking agent metoprolol and its metabolite, metoprolol acid. O-desmethylvenlafaxine, despite its very low biodegradability in conventional wastewater treatment plants, was removed to certain extent (13-39 %). Biomass concentrations suggested that bioadsorption/bioaccumulation to microalgae biomass was decisive regarding the elimination of non-biodegradable compounds such as venlafaxine and its main metabolites. HRAP treatment with and without primary treatment did not yield significant differences in terms of PhACs removal efficiency. The implementation of HRAPs as secondary treatment is a feasible alternative to CAS in terms of overall wastewater treatment, including organic micropollutants, with generally higher removal performances and implying a green, low-cost and more sustainable technology.

Natural pigments from microalgae grown in industrial wastewater.

The aim of this study was to investigate the cultivation of Nostoc sp., Arthrospira platensis and Porphyridium purpureum in industrial wastewater to produce phycobiliproteins. Initially, light intensity and growth medium composition were optimized, indicating that light conditions influenced the phycobiliproteins production more than the medium composition. Conditions were then selected, according to biomass growth, nutrients removal and phycobiliproteins production, to cultivate these microalgae in food-industry wastewater. The three species could efficiently remove up to 98%, 94% and 100% of COD, inorganic nitrogen and PO43--P, respectively. Phycocyanin, allophycocyanin and phycoerythrin were successfully extracted from the biomass reaching concentrations up to 103, 57 and 30 mg/g dry weight, respectively. Results highlight the potential use of microalgae for industrial wastewater treatment and related high-value phycobiliproteins recovery.

Pretreatment and co-digestion of microalgae, sludge and fat oil and grease (FOG) from microalgae-based wastewater treatment plants.

The aim of this study was to assess the co-digestion of residual biomass flows generated in microalgae-based wastewater treatment plants: microalgae, primary sludge and fat, oil and grease (FOG), with and without microalgae thermal pretreatment. The results evidenced the high methane yield of FOG (563 mL CH4/g VS) as compared to microalgae (140 mL CH4/gVS) and sludge (299 mL CH4/g VS). The methane yield of microalgae and sludge co-digestion (50-50% VS) was increased by 25 and 42% by adding 10 and 20% VS of FOG, respectively. Moreover, co-digestion trials improved the anaerobic digestion first-order kinetics by up to 67%. Regarding the thermal pretreatment, it increased the methane yield of microalgae by 60%, and 15% upon co-digestion with sludge and FOG. Therefore, co-digestion of microalgae, primary sludge and FOG appears as a promising strategy to enhance the biogas production, hence bioenergy recovery from wastewater, even without pretreatment.

Constructed wetlands for winery wastewater treatment: A comparative Life Cycle Assessment.

A Life Cycle Assessment was carried out in order to assess the environmental performance of constructed wetland systems for winery wastewater treatment. In particular, six scenarios which included the most common winery wastewater treatment and management options in South-Western Europe, namely third-party management and activated sludge systems, were compared. Results showed that the constructed wetland scenarios were the most environmentally friendly alternatives, while the third-party management was the worst scenario followed by the activated sludge systems. Specifically, the potential environmental impacts of the constructed wetlands scenarios were 1.5-180 and 1-10 times lower compared to those generated by the third-party and activated sludge scenarios, respectively. Thus, under the considered circumstances, constructed wetlands showed to be an environmentally friendly technology which helps reducing environmental impacts associated with winery wastewater treatment by treating winery waste on-site with low energy and chemicals consumption.

The effect of primary treatment of wastewater in high rate algal pond systems: Biomass and bioenergy recovery.

The aim of this study was to assess the effect of primary treatment on the performance of two pilot-scale high rate algal ponds (HRAPs) treating urban wastewater, considering their treatment efficiency, biomass productivity, characteristics and biogas production potential. Results indicated that the primary treatment did not significantly affect the wastewater treatment efficiency (NH4+-N removal of 93 and 91% and COD removal of 62 and 65% in HRAP with and without primary treatment, respectively). The HRAP without primary treatment had higher biodiversity and productivity (20 vs. 15 g VSS/m2d). Biomass from both systems presented good settling capacity. Results of biochemical methane potential test showed that co-digesting microalgae and primary sludge led to higher methane yields (238-258 mL CH4/g VS) compared with microalgae mono-digestion (189-225 mL CH4/g VS). Overall, HRAPs with and without primary treatment seem to be appropriate alternatives for combining wastewater treatment and bioenergy recovery.

Co-digestion of microalgae and primary sludge: Effect on biogas production and microcontaminants removal.

Microalgal-based wastewater treatment plants are conceived as low cost and low energy consuming systems. The operation of these plants involves the management of primary sludge and microalgal biomass. The aim of this study is to analyse the anaerobic co-digestion of both by-products in terms of biogas production and contaminants of emerging concern removal. The co-digestion of microalgae and primary sludge (25/75% on a volatile solids basis) was investigated in continuous reactors and compared to microalgae mono-digestion at a hydraulic retention time of 20days. Results showed how the co-digestion enhanced the anaerobic digestion of microalgal biomass, since primary sludge is a more readily biodegradable substrate, which increased the methane production by 65% and reduced the risk of ammonia toxicity. Regarding the contaminants, musk fragrances (galaxolide and tonalide) and triclosan showed the highest abundance on primary sludge (0.5-25µg/g TS), whereas caffeine, methyl dihydrojasmonate and triphenyl phosphate were barely detected in both substrates (<0.1µg/g TS). The removal of these contaminants was compound-depending and ranged from no removal to up to 90%. On the whole, microalgae mono-digestion resulted in a higher removal of selected contaminants than the co-digestion with primary sludge.

Evaluating environmental benefits of low-cost biogas digesters in small-scale farms in Colombia: A life cycle assessment.

The aim of this study was to assess the environmental benefits of implementing low-cost digesters in small-scale farms in Colombia by using the LCA methodology. Four scenarios were taken into account considering two small-scale farms located in different areas: two (previous) scenarios where manure was stored in a manure pit and liquefied petroleum gas (LPG) was used for cooking; and two (current) scenarios where manure is treated in low-cost digesters, the digestate replaces the synthetic fertiliser and the biogas is used for cooking replacing the LPG. Results showed that digesters implementation considerably reduced (by up to 80%) potential environmental impacts associated with manure handling, fuel and fertiliser use in the small-scale Colombian farms. This was mainly due to the reduction of LPG and synthetic fertiliser use which were replaced by biogas and digestate. An economic assessment showed that low-cost digesters reduced expenses associated with cooking fuel and fertiliser purchase by 80%.

Contaminants removal and bacterial activity enhancement along the flow path of constructed wetland microbial fuel cells.

Microbial fuel cells implemented in constructed wetlands (CW-MFCs), albeit a relatively new technology still under study, have shown to improve treatment efficiency of urban wastewater. So far the vast majority of CW-MFC systems investigated were designed as lab-scale systems working under rather unrealistic hydraulic conditions using synthetic wastewater. The main objective of this work was to quantify CW-MFCs performance operated under different conditions in a more realistic setup using meso-scale systems with horizontal flow fed with real urban wastewater. Operational conditions tested were organic loading rate (4.9 ±â€¯1.6, 6.7 ±â€¯1.4 and 13.6 ±â€¯3.2 g COD/m2·day) and hydraulic regime (continuous vs. intermittent feeding) as well as different electrical connections: CW control (conventional CW without electrodes), open-circuit CW-MFC (external circuit between anode and cathode not connected) and closed-circuit CW-MFC (external circuit connected). Eight horizontal subsurface flow CWs were operated for about four months. Each wetland consisted of a PVC reservoir of 0.193 m2 filled with 4/8 mm granitic riverine gravel (wetted depth 25 cm). All wetlands had intermediate sampling points for gravel and interstitial liquid sampling. The CW-MFCs were designed as three MFCs incorporated one after the other along the flow path of the CWs. Anodes consisted of gravel with an incorporated current collector (stainless steel mesh) and the cathode consisted of a graphite felt layer. Electrodes of closed-circuit CW-MFC systems were connected externally over a 220â€¯Ω resistance. Results showed no significant differences between tested organic loading rates, hydraulic regimes or electrical connections, however, on average, systems operated in closed-circuit CW-MFC mode under continuous flow outperformed the other experimental conditions. Closed-circuit CW-MFC compared to conventional CW control systems showed around 5% and 22% higher COD and ammonium removal, respectively. Correspondingly, overall bacteria activity, as measured by the fluorescein diacetate technique, was higher (4% to 34%) in closed-circuit systems when compared to CW control systems.

Strategies to Optimize Microalgae Conversion to Biogas: Co-Digestion, Pretreatment and Hydraulic Retention Time.

This study aims at optimizing the anaerobic digestion (AD) of biomass in microalgal-based wastewater treatment systems. It comprises the co-digestion of microalgae with primary sludge, the thermal pretreatment (75 °C for 10 h) of microalgae and the role of the hydraulic retention time (HRT) in anaerobic digesters. Initially, a batch test comparing different microalgae (untreated and pretreated) and primary sludge proportions showed how the co-digestion improved the AD kinetics. The highest methane yield was observed by adding 75% of primary sludge to pretreated microalgae (339 mL CH4/g VS). This condition was then investigated in mesophilic lab-scale reactors. The average methane yield was 0.46 L CH4/g VS, which represented a 2.9-fold increase compared to pretreated microalgae mono-digestion. Conversely, microalgae showed a low methane yield despite the thermal pretreatment (0.16 L CH4/g VS). Indeed, microscopic analysis confirmed the presence of microalgae species with resistant cell walls (i.e., Stigioclonium sp. and diatoms). In order to improve their anaerobic biodegradability, the HRT was increased from 20 to 30 days, which led to a 50% methane yield increase. Overall, microalgae AD was substantially improved by the co-digestion with primary sludge, even without pretreatment, and increasing the HRT enhanced the AD of microalgae with resistant cell walls.

Life cycle assessment of high rate algal ponds for wastewater treatment and resource recovery.

The aim of this study was to assess the potential environmental impacts associated with high rate algal ponds (HRAP) systems for wastewater treatment and resource recovery in small communities. To this aim, a Life Cycle Assessment (LCA) was carried out evaluating two alternatives: i) a HRAP system for wastewater treatment where microalgal biomass is valorized for energy recovery (biogas production); ii) a HRAP system for wastewater treatment where microalgal biomass is reused for nutrients recovery (biofertilizer production). Additionally, both alternatives were compared to a typical small-sized activated sludge system. An economic assessment was also performed. The results showed that HRAP system coupled with biogas production appeared to be more environmentally friendly than HRAP system coupled with biofertilizer production in the climate change, ozone layer depletion, photochemical oxidant formation, and fossil depletion impact categories. Different climatic conditions have strongly influenced the results obtained in the eutrophication and metal depletion impact categories. In fact, the HRAP system located where warm temperatures and high solar radiation are predominant (HRAP system coupled with biofertilizer production) showed lower impact in those categories. Additionally, the characteristics (e.g. nutrients and heavy metals concentration) of microalgal biomass recovered from wastewater appeared to be crucial when assessing the potential environmental impacts in the terrestrial acidification, particulate matter formation and toxicity impact categories. In terms of costs, HRAP systems seemed to be more economically feasible when combined with biofertilizer production instead of biogas. On the whole, implementing HRAPs instead of activated sludge systems might increase sustainability and cost-effectiveness of wastewater treatment in small communities, especially if implemented in warm climate regions and coupled with biofertilizer production.