Giardia Cysts and Cryptosporidium Oocysts in Membrane-Filtered Municipal Wastewater Used for Irrigation

Abstract

A wastewater tertiary treatment system based on membrane ultrafiltration and fed with secondary-treated municipal wastewater was evaluated for its Giardia cyst and Cryptosporidium oocyst removal efficiency. Giardia duodenalis (assemblages A and B) and Cryptosporidium parvum were identified in feed water but were found in filtered water only during occasional failure of the filtration system.Treated wastewater can be utilized as an alternative water source for agricultural irrigation, but advanced treatment is required to minimize its potentially negative impact on public health. In particular, chlorine-based disinfection tools cannot destroy the resistant stages of protozoan parasites Giardia and Cryptosporidium (7, 11), and there is an urgent need for specific treatments to remove these protozoa from wastewater. Membrane technologies have a strong potential in this respect, and ultrafiltration (pore size of 0.002 to 0.1 m) can achieve complete removal of protozoan cysts (4 to 15 m) by physical sieving (2, 16). This is especially interesting for wastewater reclamation and makes it possible to avoid chemical disinfection and consequent possible formation of toxic by-products (14).In a previous investigation, a pilot-scale membrane system was evaluated for reuse of treated wastewater in irrigation and gave very good performances in terms of suspended solids and bacterial removal (17). This work refers to the same experimental plant and reports results on (i) the presence of Giardia cysts and Cryptosporidium oocysts in well water used for irrigation in southern Italy and in secondary-treated wastewater from urban areas, (ii) the (oo)cyst removal efficiency of the tertiary treatment system based on membrane filtration, and (iii) the presence of (oo)cysts in soil and vegetables irrigated with well water and water filtered by the above-mentioned method.Wastewater tertiary treatment was carried out at the pilot scale by membrane ultrafiltration using a submerged hollowfiber system. All details of the pilot plant, equipped with a Zenon ZeeWeed membrane module (Zenon Environmental Inc., Canada), were provided in a previous article (17). A simplified scheme of the pilot plant is shown in Fig. 1. The permeate after filtration was collected and stored in six tanks (5 m 3 each). Although each irrigation required about 15 m 3 of water, a total stored volume of 30 m 3 was always available in order to match the continuous plant operation with the discontinuous demand for treated water for irrigation and to have a buffer of treated water in case of possible equipment failures. The test field was located about 100 m from the pilot plant and was connected to the storage tanks by a pipeline. In this experimental field, 2-year studies were carried out to compare, on four crops in succession (fennel, lettuce, chicory, and processing tomato), two types of water: tertiary filtered municipal wastewater and well water commonly used for irrigation.Giardia cyst and Cryptosporidium oocyst detection in water and wastewater was performed acco...

Risk assessment of Giardia from a full scale MBR sewage treatment plant caused by membrane integrity failure

“…However, our study showed that high concentrations of Giardia (>4 μm) could occur in the MBR effluent caused by membrane integrity failure. Lonigro et al (2006) also found Giardia and Cryptosporidium in filtered water during occasional failure of the ultrafiltration system for treating secondary effluent.…”

“…This could cause particular concerns over the release of pathogens when membrane integrity failure occurs, as pathogens may be concentrated in activated sludge in an MBR system. Lonigro et al (2006) also detected Giardia and Cryptosporidium in filtered water from an MBR during occasional failure of the ultrafiltration system for treating secondary effluent. Therefore, it will be of importance to assess the risk of Giardia in MBR effluents when a membrane loses its integrity.…”

“…In particular, occasional failure of MBR systems may cause serious problems since many pathogens -mainly viruses and protozoa -can accumulate in activated sludge at high concentrations due to the long sludge retention times usually adopted in the process (Marti et al, 2011). Leakage of Giardia cysts could be reduced by maintaining membrane integrity (Lonigro et al, 2006).…”

“…On the other hand, physical disinfection using membrane filtration has recently been a focus because theoretically it could intercept almost all of the particles larger than its pore size, including pathogenic microbes (Lonigro et al, 2006). The combination of biological wastewater treatment and membrane separation, known as the membrane bioreactor (MBR) process, has attracted particular interest because of its advantages in achieving nutrient removal and disinfection in only one step (Jefferson et al, 2000).…”

The investigation of Cryptosporidium spp. in water samples by PCR

“…are transmitted to humans via consumption of contaminated water and food but also by direct contact with infected hosts. A marked increase in the incidence of cryptosporidiosis associated with the contamination of environmental water with human and animal feces has been reported [1][2][3][4][5] , while cases of co-infection with Giardia intestinalis have been also described [6][7][8][9] . The first outbreak of human cryptosporidiosis is reported from United States in 1984, and later from several other countries worldwide [10][11][12][13][14] .…”