Role of Nannochloropsis salina for the recovery and persistence of MS2 virus in wastewater

Partitioning and inactivation of enveloped and nonenveloped viruses in activated sludge, anaerobic and microalgae-based wastewater treatment systems

Anaerobic and microalgae-based technologies for municipal wastewater treatment have emerged as sustainable alternatives to activated sludge systems. However, viruses are a major sanitary concern for reuse applications of liquid and solid byproducts from these technologies. To assess their capacity to reduce viruses during secondary wastewater treatment, enveloped Phi6 and nonenveloped MS2 bacteriophages, typically used as surrogates of several types of wastewater viruses, were spiked into batch bioreactors treating synthetic municipal wastewater (SMWW). The decay of Phi6 and MS2 in anaerobic and microalgae-based reactors was compared with the decay in activated sludge batch reactors for 96 h (Phi6) and 144 h (MS2). In each reactor, bacteriophages in the soluble and solids fractions were titered, allowing the assessment of virus partitioning to biomass over time. Moreover, the influence of abiotic conditions such as agitation, oxygen absence and light excess in activated sludge, anaerobic and microalgae reactors, respectively, was assessed using dedicated SMWW control reactors. All technologies showed Phi6 and MS2 reductions. Phi6 was reduced in at least 4.7 to 6.5 log10 units, with 0 h concentrations ranging from 5.0 to 6.5 log10 PFU mL-1. Similarly, reductions achieved for MS2 were of at least 3.9 to 7.2 log10 units, from starting concentrations of 8.0 to 8.6 log10 PFU mL-1. Log-logistic models adjusted to bacteriophages' decay indicated T90 values in activated sludge and microalgae reactors of 2.2 and 7.9 h for Phi6 and of 1.0 and 11.5 h for MS2, respectively, all within typical hydraulic retention times (HRT) of full-scale operation. In the case of the microalgae technology, T99 values for Phi6 and MS2 of 12.7 h and 13.6 h were also lower than typical operating HRTs (2-10 d), while activated sludge and anaerobic treatment achieved less than 99 % of Phi6 and 50 % of MS2 inactivation within 12 h of typical HRT, respectively. Thus, the microalgae-based treatment exhibited a higher potential to reduce the disinfection requirements of treated wastewater.

Prevalence, environmental fate, treatment strategies, and future challenges for wastewater contaminated with SARS-CoV-2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been detected in untreated and treated wastewater and studies have shown that the concentration of SARS-CoV-2 is proportional to the prevalence of the coronavirus disease 2019 (COVID-19) in communities. This article presents a literature review of the prevalence of SARS-CoV-2 in wastewater, its environmental fate, recommended treatment strategies for contaminated wastewater, and treatment challenges to be faced in the future. The environmental fate of SARS-CoV-2 in wastewater is not straightforward because it can be a source of infection when present in the treated wastewater depending on the permeability of the wastewater treatment plant containment area, and can also leach into aquifers, which may serve as drinking water supplies. Secondly, there are different practices that can mitigate the SARS-CoV-2 infection rate from infected feces and urine. The World Health Organization has recommended the use of ultraviolet radiation (UV), disinfection, and filtration for wastewater contaminated with SARS-CoV-2, processes also common in wastewater treatment facilities. This article discusses these strategies referencing studies performed with surrogate viruses and shows that SARS-CoV-2 treatment can be complicated due to the interference from other aqueous chemical and physical factors. Considering that COVID-19 is not the first and certainly not the last pandemic, it is imperative to develop an effective multitreatment strategy for wastewater contaminated with contagious viruses and, preferably, those that are compatible with current wastewater treatment methods.

The inactivation of bacteriophage MS2 by sodium hypochlorite in the presence of particles

The inactivation of bacteriophage MS2 by sodium hypochlorite was investigated to understand the effect of solution chemistry on the disinfection efficacy in the presence of particles. Kaolinite and Microcystis aeruginosa (M. aeruginosa) were used as the models of inorganic and organic particles to simulate high turbidity and algal cells, respectively, in drinking water sources. In both particle-containing solutions, lower pH, the presence of cations (di-valent Ca²⁺) and natural organic matters (NOM) were regarded as the main factors to influence the aggregation and inactivation of MS2. The results showed that MS2 aggregated in all solutions at pH 3.0, protecting the inner viruses. At pH 7.0, the presence of Na⁺ cations (0-200 mmol/L) did not affect the inactivation efficacy of MS2, which always followed the order of particles-free ≈ kaolinite > M. aeruginosa. The inactivation efficacy of MS2 in the presence of Ca²⁺ cations followed the order of kaolinite > particles-free > M. aeruginosa at 0-50 mmol/L Ca²⁺ cations, while the inactivation efficacy remained almost constant in the range of 100-200 mmol/L Ca²⁺ cations. By contrast, kaolinite offered not enough protection to adsorbed MS2, but MS2 aggregation decreased disinfection efficacy at a high concentration of Ca²⁺ cations. Moreover, the presence of humic acid as NOM decreased the inactivation of MS2 more significantly than M. aeruginosa due to the more consumption of free chlorine from humic acids. Therefore, the co-existence of NOM and di-valent Ca²⁺ cations are potential challenges for the inactivation of viruses by sodium hypochlorite in safe drinking water.