The use of solar pre-treatment as a strategy to improve the anaerobic biodegradability of microalgal biomass in co-digestion with sewage.

Sustainable sewage treatment plants (STPs) have been intensively investigated in search for low-cost, environmental-friendly options. Anaerobic-aerobic treatment solutions, as upflow anaerobic sludge blanket (UASB) reactors followed by high rate algal ponds (HRAP) have already proved to be efficient for pollutants and micropollutants removal, as well as for energy recovery from the co-digestion of raw sewage and microalgal biomass. Since microalgae cells have complex structures that make them resistant to anaerobic digestion, pre-treatment techniques may be applied to improve microalgal biomass solubilisation and methane yield. Among the thermal pre-treatments, the use of solar energy for biomass solubilisation has yet to be investigated. Therefore, this study aimed at evaluating the performance of a solar thermal microalgal biomass pre-treatment prior to the anaerobic co-digestion with raw sewage, comparing a UASB reactor feed only raw sewage and other UASB reactor feed with raw sewage and pre-treated microalgal biomass. The results showed that, the solar pre-treatment step reached an organic matter solubilisation of 32% (COD). Furthermore, the methane yield was increased by 45% (from 81 to 117 NL CH4 kg-1 COD), after the anaerobic co-digestion with pre-treated microalgae as compared to the mono-digestion of raw sewage, indicating significant difference between the evaluated UASB reactors. The energy assessment showed a positive energy balance, as the total energy produced was twice the energy consumed in the system.

Viability of SARS-CoV-2 in river water and wastewater at different temperatures and solids content.

COVID-19 patients can excrete viable SARS-CoV-2 virus via urine and faeces, which has raised concerns over the possibility of COVID-19 transmission via aerosolized contaminated water or via the faecal-oral route. These concerns are especially exacerbated in many low- and middle-income countries, where untreated sewage is frequently discharged to surface waters. SARS-CoV-2 RNA has been detected in river water (RW) and raw wastewater (WW) samples. However, little is known about SARS-CoV-2 viability in these environmental matrices. Determining the persistence of SARS-CoV-2 in water under different environmental conditions is of great importance for basic assumptions in quantitative microbial risk assessment (QMRA). In this study, the persistence of SARS-CoV-2 was assessed using plaque assays following spiking of RW and WW samples with infectious SARS-CoV-2 that was previously isolated from a COVID-19 patient. These assays were carried out on autoclaved RW and WW samples, filtered (0.22 µm) and unfiltered, at 4 °C and 24 °C. Linear and nonlinear regression models were adjusted to the data. The Weibull regression model achieved the lowest root mean square error (RMSE) and was hence chosen to estimate T90 and T99 (time required for 1 log and 2 log reductions, respectively). SARS-CoV-2 remained viable longer in filtered compared with unfiltered samples. RW and WW showed T90 values of 1.9 and 1.2 day and T99 values of 6.4 and 4.0 days, respectively. When samples were filtered through 0.22 µm pore size membranes, T90 values increased to 3.3 and 1.5 days, and T99 increased to 8.5 and 4.5 days, for RW and WW samples, respectively. Remarkable increases in SARS-CoV-2 persistence were observed in assays at 4 °C, which showed T90 values of 7.7 and 5.5 days, and T99 values of 18.7 and 17.5 days for RW and WW, respectively. These results highlight the variability of SARS-CoV-2 persistence in water and wastewater matrices and can be highly relevant to efforts aimed at quantifying water-related risks, which could be valuable for understanding and controlling the pandemic.

Reduction and partitioning of viral and bacterial indicators in a UASB reactor followed by high rate algal ponds treating domestic sewage.

Human enteric pathogens are a major global concern, as they are responsible for thousands of preventable deaths every year. New pathogens in wastewater are constantly emerging. For example, SARS-CoV-2 has been recently detected in domestic sewage and primary sludge. Knowledge about the reduction of viruses in wastewater treatment and their partitioning between the treated liquid effluent versus the sludge or biosolids is still very scarce, especially in countries with emerging economies and tropical climates. Upflow anaerobic sludge blanket (UASB) reactors are among the top three most commonly used technologies for the treatment of sewage in Latin America and the Caribbean, and their use has become increasingly common in many other low- and middle-income countries. High-rate algal ponds (HRAP) are regarded as a sustainable technology for the post-treatment of UASB effluent. This study evaluated the overall reduction and the liquid-solid partitioning of somatic coliphages, F-specific coliphages, and E. coli in a pilot-scale system comprised of a UASB reactor followed by HRAPs treating real wastewater. Average log removal for somatic and F-specific coliphages were 0.40 and 0.56 for the UASB reactor, and 1.15 and 1.70 for HRAPs, respectively. The overall removal of both phages in the system was 2.06-log. Removal of E. coli was consistently higher. The number of viruses leaving the system in the UASB solids and algal biomass was less than 10% of the number leaving in the clarified liquid effluent. The number of E. coli leaving the system in solids residuals was estimated to be approximately one order of magnitude higher than the number of E. coli leaving in the liquid effluent. Results from this study demonstrate the suitability of UASB-HRAP systems to reduce viral and bacterial indicators from domestic sewage and the importance of adequately treating sludge for pathogen reduction before they are used as biosolids.

Systematic review and meta-analysis of time-temperature pathogen inactivation.

Heat treatment, or thermal disinfection, is one of the simplest disinfection methods, and is widely used in the water, sanitation, and food sectors, especially in low resource settings. Pathogen reductions achieved during heat treatment are influenced by a combination of temperature and exposure time. The objective of this paper was to construct updated time-temperature pathogen inactivation curves to define "safety zones" for the reduction of four pathogen groups (bacteria, viruses, protozoan (oo)cysts, and helminth eggs) during heat treatment in a variety of matrices. A systematic review and meta-analysis were conducted to determine the times needed to achieve specified levels of pathogen reduction at different temperatures. Web of Science was searched using a Boolean string to target studies of heat treatment and pasteurization systems that exposed pathogens in water, wastewater, biosolids, soil, or food matrices to temperatures between 20 °C and 95 °C. Data were extracted from tables or figures and regression was used to assess the relationship between time and temperature. Our findings indicate that the temperatures and times needed to achieve a 1-log10 reduction of all pathogen groups are likely higher and longer, respectively, than previously reported. The type of microorganism and the matrix significantly impact T90 values reported at different temperatures. At high temperatures, the time-temperature curves are controlled by thermally stable viruses such as hepatitis A virus. Data gaps include the lack of data on protozoa, and the lack of data on all pathogen groups at low temperatures, for long exposure times, and with high log10 reductions. The findings from this study can be used by engineers, food safety specialists for the planning and design of engineered water, sanitation, and food pasteurization and treatment systems.

Identification of microalgae from waste stabilization ponds and evaluation of electroflotation by alternate current for simultaneous biomass separation and cell disruption / Identificação de microalgas de lagoas de estabilização e avaliação do método de eletroflotação por corrente alternada para separação e ruptura celular simultâneas

ABSTRACT This work aimed to investigate algal diversity at the genus level in stabilization pond systems treating domestic wastewater and to evaluate the feasibility of an electroflotation by alternate current (EFAC) system for simultaneous microalgae separation and cell disruption. Evaluation of algal diversity showed that the genera Euglena and Chlorella were present in relatively high frequencies in five of the six effluents analyzed. The use of EFAC on an effluent that presented bloom of Chlorella achieved turbidity and chlorophyll-a removal efficiencies higher than 70 and 90%, respectively, after 70 minutes of operation. Total lipid yield for the Chlorella-rich biomass was 21.4±2.02%. Such high biomass lipid content demonstrates the potential for obtaining lipid-based biofuels from wastes. The current paper describes the first attempt, with promising results, at using electroflotation by alternate current for low cost, simultaneous microalgae harvesting and disruption.

RESUMO Este trabalho objetivou investigar a diversidade algal no que se refere a gênero em sistemas de lagoas de estabilização tratando esgoto doméstico, bem como analisar a viabilidade de um sistema de eletroflotação por corrente alternada para obter simultaneamente separação e ruptura celular. A avaliação de diversidade algal mostrou que os gêneros Euglena e Chlorella estiveram presentes com relativamente elevada frequência em cinco dos seis efluentes analisados. A aplicação de eletroflotação por corrente alternada em um efluente que apresentou elevada predominância de Chlorella alcançou eficiências de remoção de turbidez e clorofila-a maiores que 70 e 90%, respectivamente, depois de 70 minutos de operação. O rendimento de lipídios totais para a biomassa rica em Chlorella foi de 21,4±2,02%. Esse elevado teor lipídico demonstra potencial para obtenção de biodiesel de lipídios de efluentes. O presente artigo descreve uma primeira tentativa, com resultados promissores, da utilização de eletroflotação por corrente alternada para separação e ruptura celular simultânea com baixo custo.