Innovative Treatment Technologies for Reclaimed Water

In order to meet disinfection guidelines, wastewater utilities must achieve a high level of treatment before discharging treated water for irrigation or industrial use. However, public pressure to reduce disinfection by-products and pharmaceutically-active compounds, recently-promulgated regulations on chlorine-resistant microorganisms such as Cryptosporidium parvum, and growth in population and water demand have driven an interest in alternatives to chlorination. The WateReuse Foundation has funded WRF 02-009 (Innovative Treatment Technologies for Reclaimed Water), which is a survey of current and emerging reuse water treatment technologies. The goal of the project is to evaluate treatment technologies can provide adequate recycled water effluent without the cost of reverse osmosis (RO) or the disinfection by-products (DBPs) formed during chlorination.

The inactivation of indigenous microorganisms (total and fecal coliform bacteria, and total aerobic spores) and spiked surrogate, respiratory, and enteric viruses (MS-2 bacteriophage, adenovirus type 4, reovirus type 3, and coxsackievirus type B5) and chemical degradation by wastewater treatment technologies was evaluated on the bench-scale. These include: low- and medium-pressure UV, LPUV/H₂O₂, ozonation, O₃/H₂O₂, peracetic acid (PAA), LPUV/PAA, chlorination, chloramination, and ultrafiltration. The applicability of the candidate disinfection methods, especially emerging and comparatively untested methods such as PAA and advanced oxidation processes (AOPs), was studied through comparison of their performance and the important water matrix parameters (e.g., alkalinity, BOD, TSS, etc.).

Of the chemical disinfectants, molecular ozone and free chlorine were the most effective, with substantial coliform and virus kill at low doses. Combined chlorine in the form of monochloramine had a reduced disinfectant capacity than free chlorine, and peracetic acid (PAA) performed equally as well as free chlorine with respect to coliform bacteria in some instances but had little to no impact on spiked MS2 bacteriophage. None of the aforementioned disinfectants had an appreciable impact on indigenous aerobic spore-forming bacteria due to their physiology. UV and O₃ rapidly killed human enteric and respiratory viruses, but a consistent benefit by AOPs over their base technologies was not observed for any of their base technologies.

Low and medium-pressure UV inactivated free-floating indigenous coliform bacteria almost immediately, while slower inactivation rates at higher UV fluences illustrated the "tailing" behavior observed when bacteria are embedded in or shielded by particulate matter. Log-linear inactivation of spiked viruses and indigenous aerobic spores by UV was consistent across the utility waters. The UV-based advanced oxidation processes (UV/H₂O₂ and UV/PAA) destroyed spiked organic compounds at much higher rates than direct UV photolysis, while O₃, with or without H₂O₂ , oxidized spiked compounds and reduced estrogenicity (EEQ) at low doses. Recalcitrant chlorinated hydrocarbons such as TCEP were only moderately removed by the tested AOPs, but low doses of O₃ (3 ppm residual O₃) reduced estrogenic activity by 99%. Like other disinfection processes, AOP performance is dependant on pretreatment, especially concerning particulates.