Long‐term Hygienic Barrier Efficiency of a Compact On‐site Wastewater Treatment System

Abstract

The long-term use of a filter-based, on-site wastewater treatment system increases nutrient discharge to receiving waters and may reduce its hygienic barrier efficiency. The main purpose of this research was to assess the hygienic barrier efficiency and the associated health risks of an on-site system that had exceeded its 5-yr design capacity with respect to phosphorus (P) removal. The system was investigated for bacteria and virus removal and assessed with respect to potential health risks in relation to reuse of effluent for irrigation. The system consists of a septic tank, a pressure-dosed vertical flow biofilter, and an up-flow filter unit with lightweight clay aggregates. The total P concentration in the effluent had increased gradually from initially <0.1 mg P L(-1) during the first 2 yr of operation to 1.8 mg P L(-1) after 5.3 yr. Escherichia coli was used as an indicator organism for fecal bacteria removal, whereas bacteriophages phiX174 and Salmonella typhimurium phage 28B (S.t. 28B) were used to model enteric virus removal. An overall decrease in E. coli removal occurred from a complete (approximately 5.6 log10) reduction during the first 3 yr of operation to 2.6 log10 reduction. The removal amounts of the bacteriophages phiX174 and S.t. 28B were 3.9 and 3.7 log10, respectively. Based on removal of S.t. 28B, the risks of rotavirus infection and disease for the investigated scenarios were above the acceptable level of 10(-4) and 10(-3), respectively, as defined by the World Health Organization.

Quality of greywater treated in biochar filter and risk assessment of gastroenteritis due to household exposure during maintenance and irrigation

“…For example, Heistad et al . () reported that the median P I‐annual of rotavirus for exposure through direct contact during irrigation with treated sewage water and consumption of lettuce was 10 − 1 to 10 − 2 , which is similar to that found in the present study for rotavirus (10 − 1 to 10 − 3 ).…”

“…as suggested by Heistad et al . (). This equation allowed estimation of concentration of pathogens considering the faecal input only from the infected persons: where CP is the concentration of the pathogen (CFU or PFU l −1 ), PD is pathogen density in the faeces, also referred to as excretion rate of pathogen in faeces (CFU or PFU g −1 ), YI is number of infection episodes per year per person, ET is the pathogen excretion time (days), UR is the underreporting ratio of disease incidence and NIP is the number of infected persons (Table ).…”

Septic Systems

“…effluent filters, to guarantee effective removal of pathogens and other pollutants (Heistad et al, 2009). For example, in a study to assess removal of phosphorus, bacteria, and viruses by an onsite system containing a septic tank, a pressure-dosed vertical flow biofilter, and an upflow filter unit with lightweight clay aggregates a progressively decreased phosphorus removal by the filters in the end of and after a 5-year design capacity was exceeded (Heistad et al, 2009). In addition, there was a substantial decrease in the removal efficiency of E. coli during three years of operation, from 5.6 log 10 to 2.6 log 10 reduction.…”

Rotavirus and Astrovirus

“…The long-term use of a filter-based, on-site wastewater treatment system increases nutrient discharge to receiving waters and may reduce its hygienic barrier efficiency. In Norway, based on removal of bacteriophages, it was estimated high RVA infection risk (>1/10,000 per annum) for children that accidentally ingest 1-2 mL of the effluent of a septic tank receiving wastewater from single households (Heistad et al, 2009).…”