Hygienic assessment of digestate from a high solids anaerobic co-digestion of sewage sludge with biowaste by testing Salmonella Typhimurium, Escherichia coli and SARS-CoV-2

SARS-CoV-2 in the environment: Contamination routes, detection methods, persistence and removal in wastewater treatment plants

The present study reviewed the occurrence of SARS-CoV-2 RNA and the evaluation of virus infectivity in feces and environmental matrices. The detection of SARS-CoV-2 RNA in feces and wastewater samples, reported in several studies, has generated interest and concern regarding the possible fecal-oral route of SARS-CoV-2 transmission. To date, the presence of viable SARS-CoV-2 in feces of COVID-19 infected people is not clearly confirmed although its isolation from feces of six different patients. Further, there is no documented evidence on the infectivity of SARS-CoV-2 in wastewater, sludge and environmental water samples, although the viral genome has been detected in these matrices. Decay data revealed that SARS-CoV-2 RNA persisted longer than infectious particle in all aquatic environment, indicating that genome quantification of SARS-CoV-2 does not imply the presence of infective viral particles. In addition, this review also outlined the fate of SARS-CoV-2 RNA during the different steps in the wastewater treatment plant and focusing on the virus elimination along the sludge treatment line. Studies showed complete removal of SARS-CoV-2 during the tertiary treatment. Moreover, thermophilic sludge treatments present high efficiency in SARS-CoV-2 inactivation. Further studies are required to provide more evidence with respect to the inactivation behavior of infectious SARS-CoV-2 in different environmental matrices and to examine factors affecting SARS-CoV-2 persistence.

Changes in bacterial diversity, co-occurrence pattern, and potential pathogens following digestate fertilization: Extending pathogen management to field for anaerobic digestion of livestock manure

Digestate can spread pathogens into agroecosystem, posing serious threats to public health. However, the effect of digestate fertilization on digestate- or soil-borne pathogens has not been fully explored. Herein, two settings of microcosm experiment were performed with arable soil and digestate collected at two sites (Beilangzhong or Shunyi) to dissect the succession of the total and potential pathogenic bacterial communities following digestate fertilization. Each experimental setting consisted of three treatments, including digestate aerobically incubated in sterilized soil, and soil amended with sterilized or non-sterilized digestate. Digestate-borne potential pathogenic bacteria were enriched after the aerobic incubation, with Streptococcus sobrinus in the Beilangzhong setting, and Escherichia coli and Enterococcus faecium in the Shunyi setting. Potential soil-borne pathogenic bacteria, such as Acinetobacter lowffii and Pseudomonas fluorescens, were stimulated by the sterilized digestate in the Shunyi setting. Interestingly, S. sobrinus, E. coli, and Ent. faecium did not increase when digestate was amended into the non-sterilized soil, suggesting that soil microorganisms can inhibit the resurgence of these digestate-borne pathogens. A large-scale survey further revealed that organic fertilization exerted a site-dependent effect on different species of potential pathogen, but it did not enrich the total relative abundance of potential pathogenic bacteria in soils. Collectively, these results highlight that pathogen management of anaerobic digestion of livestock manure needs to be extended from anaerobic reactor to field.

Recent Research on Municipal Sludge as Soil Fertilizer in China: a Review

Due to the annual increase in wastewater treatment in most Chinese cities, a major environmental issue has arisen: safe treatment, disposal, and recycling of municipal sludge. Municipal sludge has a high content of carbon and essential nutrients for plant growth; hence, it has gained interest among researchers as a soil fertilizer. This study discusses the potential usage of municipal sludge as soil fertilizer (indicators include nitrogen (N), phosphorus (P), and trace elements) along with its shortcomings and drawbacks (potentially toxic elements (PTEs), organic matter (OM), pathogens, etc.) as well as reviews the latest reports on the role of municipal sludge in land use. The use of municipal sludge as a soil fertilizer is a sustainable management practice and a single application of sludge does not harm the environment. However, repeated use of sludge may result in the accumulation of harmful chemicals and pathogens that can enter the food chain and endanger human health. Therefore, long-term field studies are needed to develop ways to eliminate these adverse effects and make municipal sludge available for agricultural use.