Pathogens and fecal indicators in waste stabilization pond systems with direct reuse for irrigation: Fate and transport in water, soil and crops

Abstract

Wastewater use for irrigation is expanding globally, and information about the fate and transport of pathogens in wastewater systems is needed to complete microbial risk assessments and develop policies to protect public health. The lack of maintenance for wastewater treatment facilities in low-income areas and developing countries results in sludge accumulation and compromised performance over time, creating uncertainty about the contamination of soil and crops. The fate and transport of pathogens and fecal indicators was evaluated in waste stabilization ponds with direct reuse for irrigation, using two systems in Bolivia as case studies. Results were compared with models from the literature that have been recommended for design. The removal of Escherichia coli in both systems was adequately predicted by a previously-published dispersed flow model, despite more than 10years of sludge accumulation. However, a design equation for helminth egg removal overestimated the observed removal, suggesting that this equation may not be appropriate for systems with accumulated sludge. To assess the contamination of soil and crops, ratios were calculated of the pathogen and fecal indicator concentrations in soil or on crops to their respective concentrations in irrigation water (termed soil-water and crop-water ratios). Ratios were similar within each group of microorganisms but differed between microorganism groups, and were generally below 0.1mLg(-1) for coliphage, between 1 and 100mLg(-1) for Giardia and Cryptosporidium, and between 100 and 1000mLg(-1) for helminth eggs. This information can be used for microbial risk assessments to develop safe water reuse policies in support of the United Nations' 2030 Sustainable Development Agenda.

Contribution of Wastewater Irrigation to Soil Transmitted Helminths Infection among Vegetable Farmers in Kumasi, Ghana

“…To safeguard human health, the WHO formulated guidelines for the use of wastewater in unrestricted agriculture [4], with a guideline value of <1 ova/L aimed at reducing the risk of infection. In this study, the mean concentration of STHs ova was higher than the recommended guideline value, especially for Ascaris spp (2.62 ova/L and 2.82 ova/L for dry and wet seasons, respectively) and hookworm (2.05 ova/L in the wet season), in line with similar results reported from studies in Ghana [3, 19, 20, 29] as well as other countries [25, 30, 35]. There was seasonal variation in the mean concentration of the STHs ova in the irrigation water, with the wet season showing higher concentrations than the dry season.…”

Empirical Characterization of Particle Size Distribution Spatial Dynamics for Helminth Eggs Detection in Waste Stabilization Ponds (WSP)

“…This asks for developing an inverse modelling technique for reconstructing the particle density distribution starting from the PSD difference at the top and the bottom and the travel times where sedimentation can occur. Travel times (which result in the HRT of the pond) are crucial to the operation of WSP [14][15][16], and therefore the next task will be the development of a hydraulic model in Delft3D that is able to capture actual flow conditions in the Buguruni WSP. The PSD data presented here will be used, together with a hydrodynamic model developed in Delft3D, to derive the range of densities of wastewater particles at different nodes in the Buguruni WSP and hence trace where helminth eggs are most likely to be found.…”

“…Complete removal of the eggs is by sedimentation in waste stabilization ponds (WSP) [8][9][10][11] when a hydraulic retention time (HRT) of about 20 days has been achieved [9,12,13]. However, actual HRT in WSP is normally lower than the designed HRT, thereby compromising their performance [14][15][16], including the removal of helminth eggs [16]. Moreover, WSP are not designed for sedimentation, despite the universal acceptance that this is the main mechanism for helminth eggs removal, as well as a large percent of other pollutants.…”

Achilles heel of environmental risk from recycling of sludge to soil as amendment: A summary in recent ten years (2007–2016)

“…Pathogen microorganism in sludge and the change in vitality when sludge is harmless treated followed by being recycled to soil Sludge contains broad-spectrum profile of pathogenic microorganisms due to originating from domestic sewage, which is abundant in all kinds of bacteria (Arora et al, 2014;Li et al, 2015;Scheinemann et al, 2015), such as fecal coliform (Cabanas-Vargas et al, 2013;Ozdemir et al, 2013;Rhodes et al, 2015), Salmonella coli (Bonetta et al, 2014;Cabanas-Vargas et al, 2013;Levantesi et al, 2015), Escherichia coli (Levantesi et al, 2015;Verbyla et al, 2016;Pascual-Benito et al, 2015). In addition, there are a plenty of ascaris egg in sludge because most of its solid constitute is mainly from human faeces (Darimani et al, 2016;Verbyla et al, 2016;Fidjeland et al, 2015Fidjeland et al, , 2013. Main pretreatment measures are usually employed prior to recycling to soil, such as aerobic compost and anaerobic digestion, which are effective in inactivating or eliminating most of their vitalities (Cabanas-Vargas et al, 2013;Kjerstadius et al, 2013;Sreesai et al, 2013).…”