Bio-filtration of helminth eggs and coliforms from municipal sewage for agricultural reuse in Peru

Where fresh water resources are scarce, treated wastewater becomes an attractive alternative for agricultural irrigation. However, the presence of large amounts of pathogens, even in treated wastewater, constraints its productive use, which is aggravated when sanitation and public health are poor. Among pathogenic indicators, helminth eggs are one of the most persistent microorganisms in treated effluents that may survive for several months in the irrigated fields. Application of upflow anaerobic sludge blanket (UASB) reactors could contribute to decrease the pathogenic content in wastewater due to physical and biological interactions with the anaerobic sludge bed, such as filtration and entrapment. In this thesis, the potential of the anaerobic sludge bed to particularly remove helminth eggs, was investigated in four phases. In the first phase, a temperature of 4° C was fixed in the UASB reactors in order to reduce the biological activity of the sludge. Hence, the anaerobic sludge filtration capacity at different upflow velocities was studied. This phase of the research was performed in two experiments. The first one using latex beads, simulating helminth eggs, and the second one using real helminth eggs, predominating in Peruvian wastewater. First experimental results show that increasing the upflow velocity led to a decrease in the removal efficiency of latex beads. At the lowest upflow velocity of 0.3 m·h−1, 100% removal of latex beads was reached. At an upflow velocity higher than 1 m·h−1, the removal efficiency dropped under 90 %. The degree of stabilisation of the sludge nor the sludge bed volume did not have a significant effect. Second experiment's results show that with upflow velocities below 1.5 m·h−1 real helminth eggs removal is greater than 70 %. Simultaneously tested, total and faecal coliforms removal was less than 83 %. The most common helminth eggs species found in the studied wastewater were Ascaris lumbricoides, Trichuris spp. and Strongyloides spp. The second phase was performed using two lab-scale UASB reactors at average ambient temperatures between 16.7 °C and 28.5 °C in the city of Lima (Peru). Ascaris suum eggs originating from infected pigs were selected as model organisms, considering their similarity, in terms of size and morphology, with Ascaris lumbricoides, a human pathogen. The sludge filtration capacity was determined, applying upflow velocities between 0.09 and 0.68 m·h−1. Average helminth eggs removals varied between 26 and 93 %, depending on upflow velocity and sludge bed height. 93 % removal was achieved when applying an upflow velocity of 0.09 m·h−1 and a sludge bed height reaching 19-25 % of the total reactor height. The third phase was conducted to test the effect of lower operational temperatures in the UASB reactor on the pathogen removal from domestic wastewater. Thus, a lab scale UASB reactor in the city of Puno (Peru), treating wastewater with temperatures varying between 11.3 and 14.3 °C for a period of 22 weeks after the start-up of the reactor, was used. Upflow velocities varied between 0.12 and 0.41 m·h−1. Results confirmed outcomes of the first phase of this research concerning helminth eggs removal, and consequently show that the sludge bed filtration capacity varied between 89 and 95 %. Faecal coliform removal varied between 0.9 and 2.1 log10 and E. coli removal between 0.8 and 1.6 log10. In general, removal efficiencies regarding helminth eggs and faecal coliforms, are not sufficient to comply with reuse standards. Finally, the capacity of Down Flow Hanging Sponge (DHS) reactors for removing faecal coliforms from domestic UASB reactor effluent for agricultural reuse in developing countries was investigated. Applied reactors were the cube type DHS (G1) without recirculation, the cube type DHS (G1) with recirculation and the curtain type DHS (G2). Results reveal an average faecal coliform removal of 4.74, 3.42 and 1.25 log10 respectively. These results comply with categories A, B and C of WHO (1989) standards, correspondingly. Therefore, treatment trains consisting of UASB-DHS reactors can possibly be applied when agricultural reuse is contemplated.