Environmental assessment of on-site source-separated wastewater treatment and reuse systems for resource recovery in a sustainable sanitation view.

Sustainable sanitation solutions are necessary for promoting public health and environmental security. In this study, on-site domestic wastewater treatment (WWT) systems used for households in rural and peri-urban areas of Brazil were compared in different scenarios from a life cycle assessment (LCA) perspective. The evaluated scenarios represented different practices in wastewater management, such as direct discharge into the soil, rudimentary treatment, septic tank, public sewerage system, and source separation of wastewater streams for water, nutrient, and organic matter recovery. The WWT technologies considered in the proposed scenarios of source-separated wastewater streams were as follows: an evapotranspiration tank (TEvap) and composting toilet for blackwater, a modified constructed wetland (EvaTAC) for greywater, and a storage tank for urine. LCA was performed in this study according to the ISO standards to assess the environmental impacts at both midpoint and endpoint levels. The results show that on-site source-separated wastewater treatment systems with resource recovery result in significant reductions in environmental impacts compared to scenarios with precarious conditions or 'end-of-pipe' solutions. For example, regarding the human health damage category, the scenarios involving resource recovery, including systems such as EvaTAC, TEvap, composting toilet, and urine storage tank, demonstrate significantly lower values (-0.0117 to -0.0115 DALY) compared to scenarios with rudimentary cesspits and septic tanks (0.0003 to 0.001 DALY). We conclude that the focus should be beyond mere pollution aspects and instead concentrate on the benefits of the co-products, which are: avoiding the extraction and consumption of valuable and increasingly scarce raw materials, such as potable water, and production of synthetic fertilizer. Furthermore, it is highly recommended that an LCA of sanitation systems synergistically integrates the WWT process, the constructive aspects, and the resource recovery potential.

Change in microbial profile and environmental conditions in a constructed wetland system treating greywater.

The objective of this work was to verify the relationships between environmental conditions and microbial processes along a raw-light greywater flow in an improved constructed wetland (CW) system. Physicochemical analysis and high-throughput DNA sequencing were performed in the different zones to investigate the environmental conditions and microbial communities. The results showed that the system operated predominantly under anaerobic conditions, with redox potential (Eh) increasing from the inlet (-342.9 mV) to the outlet (-316.4 mV). Conversely, the chemical oxygen demand (COD) decreased along the greywater flow, suggesting negative correlation between these characteristics. The zones of the evapotranspiration and treatment tank (CEvaT) were characterized by lower community diversity and richness and by the presence of specific groups: Proteobacteria and Synergistetes related to the first steps of the conversion of organic carbon, in the bottom layer inside the anaerobic chamber (AnC); methanogens (Methanosaeta and Methanobacterium) and sulphate-reducing bacteria (Desulfovibrio, Desulforhabdus and Desulfomonile) in the middle layer; and microorganisms associated with the nitrogen cycle and oxygen release (Acinetobacter, Novosphingobium, Candidatus Nitrososphaera) in the top layer. On the other hand, the increase of the ORP and decrease of organic matter concentrations were associated with higher community diversity and richness in the middle layer of the CW, which showed higher abundance of microorganisms involved in methane (Methylobacterium and Candidatus Koribacter) and sulphur (Rhodoblastus and Thiobacillus) oxidation.

Evaluation of biomethanization during co-digestion of thermally pretreated microalgae and waste activated sludge, and estimation of its kinetic parameters.

The maximum methane yield that can be obtained from anaerobic co-digestion of microalgae and waste activated sludge (WAS) mixtures, after thermal pretreatment at 65 °C during 4 h, was investigated. Furthermore, the fitting of the experimental data by five kinetic models (first-order, second-order, modified Gompertz, Logistic, and two-substrate) was evaluated. Thermal pretreatment increased the methane yield of single microalgae and WAS digestion by ≈ 44 and by ≈ 52%, respectively. The results also showed that up to 60% of WAS can be co-digested with microalgae without impairing the methane yield, producing up to 338 mLCH4 gVS-1. Data from digestion of non-pretreated microalgae and WAS were well described by all kinetic models, but digestion of thermally pretreated microalgae, WAS, and their co-digestion mixtures, was best fitted by means of a two-substrate model, indicating that after pretreatment it is necessary to take into account the contribution of both rapidly and slowly biodegradable fractions.

Life Cycle Assessment of prospective MSW management based on integrated management planning in Campo Grande, Brazil.

A crucial first step in transforming problematic waste management into sustainable integrated systems is comprehensive planning and analysis of environmental and socio-economic effects. The work presented here is a Life Cycle Assessment (LCA) that addressed the environmental performance of prospective development pathways for the municipal solid waste (MSW) management system in a large urban area, i.e. Campo Grande, Brazil. The research built on data and expanded the main development pathway proposed in the municipalities integrated waste management plan, which covers a period of 20 years (2017-2037). The system progression was assessed for milestone years (5-year intervals) considering projections of future population and waste generation growth, as well as addressing the development of surrounding systems, such as energy production. Results reveal that the rather conservative planned development pathway, which is largely based on gradual increase in selective collection, could successfully counter negative environmental externalities that would otherwise materialize due to increasing waste generation. A second, more ambitious, pathway with additionally scheduled actions to treat mixed MSW and upgrade certain treatment technologies (e.g. from composting to anaerobic digestion of collected organics), was used to illustrate a potential range for significantly higher impact reduction and even positive externalities, given a zero burden approach before waste generation.

Alternative use of Pseudomonas aeruginosa as indicator for greywater disinfection.

Greywater presents great potential for reuse; if treated correctly and efficiently, it can be used for several residential uses. The objective of this work was to test advanced oxidation for greywater disinfection through UV/TiO2, UV/TiO2/H2O2, photo-Fenton, UV/H2O2 and photolysis (UV) processes, using Pseudomonas aeruginosa as an alternative indicator. In general, the processes with hydrogen peroxide (150 mg.L-1) mixed in the pretreated greywater and exposed to solar radiation or artificial radiation from UV lamps were the most efficient in the disinfection experiments, with total inactivation of P. aeruginosa. These processes (UV/H2O2 and photo-Fenton) were better fitted to the log-linear/caudal decay model with remaining microorganism for the hydrogen peroxide concentration of 25 mg.L-1. The use of P. aeruginosa as an alternative indicator for the greywater disinfection was very promising due to its high resistance and high natural concentration in the effluent used in the experiments. The treatment applied with the UV/H2O2 process with the hydrogen peroxide concentration at 150 mg.L-1 was the only one that showed acute toxicity, even though it removed a good part of the surfactant concentration from the pre-treated greywater.

Desinfecção de água cinza por fotocatálise heterogênea / Disinfection of greywater by heterogeneous photocatalysis

RESUMO A desinfecção adequada de águas cinzas é necessária para garantir a segurança de sua reutilização, principalmente em aplicações com potencial de exposição humana. Diversos processos oxidativos avançados têm sido empregados nos últimos anos para a degradação de contaminantes orgânicos, bem como para desinfecção de águas e efluentes. O objetivo deste trabalho foi testar TiO2 suportado em microtubos para desinfetar águas cinzas por meio da fotocatálise heterogênea, visando ao reúso hídrico em bacia sanitária. A água cinza utilizada nos experimentos foi coletada após passar por um sistema de tratamento composto de um tanque de evapotranspiração seguido de banhado construído de fluxo horizontal. Foram realizados testes em batelada utilizando-se um reator fotoquímico cilíndrico de 1,0 L (volume total do reator), preenchido com pequenos cilindros de vidro do tipo Pyrex com TiO2 suportado. Para os testes de desinfecção, foram utilizados os processos UV, H2O2, UV/TiO2, UV/H2O2 e UV/TiO2/H2O2. Foi possível obter uma camada homogênea de TiO2 depositada nos pequenos tubos de vidro Pyrex, com espessura média de 35,3 µm, capaz de promover um incremento na desinfecção de águas cinzas. Porém, mesmo com um maior poder de desinfecção do TiO2 - se comparado com a fotólise (UV) -, os processos em que se empregou o peróxido de hidrogênio foram bem mais eficientes, tanto na desinfecção (inativação total de coliformes totais, enterococos e Pseudomonas aeruginosa) quanto na remoção de matéria orgânica em termos de demanda química de oxigênio (em torno de 60%). As amostras mantidas em temperatura ambiente e envolvidas por plástico escuro não apresentaram recrescimento bacteriano com 24h de armazenamento após os experimentos, mostrando assim a viabilidade da água cinza tratada em reúso doméstico.

ABSTRACT Proper disinfection of greywater is needed to ensure the safety of its reuse, especially in applications with potential for human exposure. Various advanced oxidation processes have been used in recent years for the degradation of organic contaminants, as well as for disinfection of water and wastewater. The purpose of this study was to test TiO2 supported in microtubes to disinfect greywater by photocatalysis in order to reuse it in sanitary bowl. The greywater used in the experiments was collected after passing through a treatment system consisting of an evapotranspiration tank followed by constructed wetland with horizontal flow. Batch tests were conducted using a cylindrical photochemical reactor of 1.0 L (total volume of the reactor), filled with small glass Pyrex cylinders with supported TiO2. For disinfection tests, the processes UV, H2O2, UV/TiO2, UV/H2O2 and UV/TiO2/H2O2 were used. It was possible to obtain a homogeneous layer of TiO2 deposited in small Pyrex glass tubes with an average thickness of 35.3 µm; this layer was able to promote an increase in the greywater disinfection. However, even with a greater disinfection power of TiO2 compared with photolysis (UV), the processes with hydrogen peroxide was much more efficient in disinfection (total inactivation of total coliforms, enterococci and Pseudomonas aeruginosa) and in the removal of organic matter in terms of chemical oxygen demand (around 60%). Samples stored at a room temperature and wrapped in plastic dark showed no bacterial regrowth after 24 hours of storage after the experiments, thus showing the viability of treated greywater for domestic reuse.

Studies of filter media for zero-discharge systems collecting light greywater.

Zero-discharge constructed wetland environments are more prone to the accumulation of pollutants. The relationship between filter media and microbial communities in this type of environment is still poorly known. We conducted bench-scale studies of different filter media (polyurethane foam, blast-furnace slag, and loofah) in these systems by simulating the batch operation with light greywater for 433 days. Physicochemical and microbiological analyses (scanning electron microscopy and polymerase chain reaction electrophoresis denaturing gradient gel) were used. In all systems, anoxic environments prevailed. These environments were crucial for methanogenesis and sulfidogenesis processes, which are primarily responsible for organic material conversion. The chemical oxygen demand/sulfate (COD/SO42-) ratio was the limiting factor in the competition of microorganisms involved in these processes. This condition, combined with the neutral-alkaline pH, also allowed Chloroflexi phylum bacteria to oxidize sulfide to sulfate and elemental sulfur in all studied media. The results showed strong evidence supporting that the microbial community formed in the present study is more related to operational/environmental conditions than to the different tested filter media. Thus, this demonstrates that the control of interactive effects between pH, redox potential, and the COD/SO42- ratio can prevent the accumulation and/or release of sulfide in anoxic environments.

Anaerobic digestion of cassava wastewater pre-treated by fungi.

Cassava wastewater (cww) contains high concentrations of easily acidifying compounds, requiring a buffered system to allow a stable operation during anaerobic digestion (AD). The possibility to include a preliminary one-step fungi treatment aimed at raising the pH and buffering the cww prior to AD was studied. Preliminary tests were performed with a naturally grown fungal mixed culture, under aerated (AE), non-aerated (NAE) and initially oxygen-deprived (IOD) conditions. The cww was pre-treated by the NAE condition, until reaching a soluble chemical oxygen demand (COD) of 10 g L(-1) and pH 6.4 (batch A) and pH 5.7 (batch B). The fungal mixed culture showed ability to biodegrade the cww with initial pH of 4.4 and 14,500 mg COD L(-1), raising the pH over 8.5, with only 13 % of COD remaining within 27 days for both AE and NAE condition. The fungal pre-treated-cww (FPTcww) was subjected to anaerobic digestion under different buffered (CaCO3 and NaHCO3) and non-buffered conditions. The FPTcww with initial pH at 6.4 provided stability during the anaerobic biodegradability tests, showing the possibility of system operation without buffer addition, with final pH around 7. The application of a fungal pre-treatment can be a promising strategy to permit the anaerobic digestion of carbohydrate-rich wastewaters.

The anaerobic conversion of methanol under thermophilic conditions: pH and bicarbonate dependence.

The thermophilic (55 degrees C) anaerobic conversion of methanol was studied in an unbuffered medium (pH 4+/-0.2) and in a phosphate buffered medium (pH 6.4+/-0.1), in both cases without bicarbonate addition. Our cultivated sludge consortium was unable to degrade methanol under acidic conditions. During the 160 d of continuous operation of an up-flow anaerobic sludge blanket (UASB) reactor (R1), at an organic loading rate (ORL) of 6 gCOD/(l.d) and pH around 4, only 5% of the applied methanol load was consumed and no methane (CH4) was detected. However, hydrogenotrophic methanogens were found to be resistant to exposure to such conditions. At the end of the trial, the hydrogenotrophic methanogenic activity of the sludge was 1.23+/-0.16 gCOD/(gVSS.d) at neutral pH. With methanol as the test substrate, the addition of bicarbonate led to acetate accumulation. A second reactor (R2) was operated for 303 d at OLRs ranging from 5.5 to 25.4 gCOD/(l.d) in order to assess the conversion of methanol at neutral pH (phosphate buffered) in a bicarbonate deprived medium. The reactor performance was poor with a methanol-COD removal capacity limited to about 9.5 gCOD/(l.d). The system appeared to be quite susceptible to any type of disturbance, even at low OLR. The fraction of methanol-COD converted to CH4 and acetate was found to be unaffected by the OLR applied. At the end of the trial, the outcome of the competition was about 50% methanogenesis and 50% homoacetogenesis.