Water Online

September 2017

Water Innovations gives Water and Wastewater Engineers and end-users a venue to find project solutions and source valuable product information. We aim to educate the engineering and operations community on important issues and trends.

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wateronline.com n Water Innovations 17 RESOURCERECOVERY separate from potable water. Single Pipe (The Future): Refresh the wastewater to where it is safe for potable water augmentation. The "Dual Pipe" approach spends less money on wastewater treatment but more on the dual-pipe distribution system, its long-term maintenance, and control of "cross connections" risk. The "Single Pipe" approach spends more money on advanced wastewater treatment but less on distribution piping and has no cross- connection concerns. Improvements in advanced wastewater treatment technologies are tilting the economics in favor of the "Single Pipe" approach. Consequently, numerous cities and towns are currently planning and implementing potable reuse projects as the more economical alternative. In implementing a One Water future, both regulators and the public are concerned about pathogens, carcinogens (such as disinfection byproducts [DBPs], pesticides, heavy metals, etc.), and chemicals of emerging concern (CECs, which include hormones, pharmaceuticals, personal care products, etc.). Pathogens, DBPs, And CECs Pathogens are the foremost concern with every reuse project, particularly One Water projects. Because no water can be tested for every possible pathogen, the regulatory community has studied the matter in detail and has developed analytical protocols that protect public health. Specifically, if removing particular indicator pathogens (e.g., Giardia lamblia, Cryptosporidium parvum, enteric viruses, and coliforms) is demonstrated, then the water is judged safe for reuse, even drinkable. The technologies to remove pathogens from drinking water standards exist and are being implemented. DBPs are commonly detected in potable water supplies, regardless of whether water reuse is involved. Common DBPs include total trihalomethanes (TTHMs), haloacetic acids (HAA5), bromate, and NDMA (N-Nitrosodimethlyamine). Control of DBPs during water treatment and distribution requires a deep understanding of DBP precursors and formation pathways. As examples, total organic carbon (TOC) is a good indicator of the presence of TTHM precursors; TTHMs can be formed during chlorine-based disinfection processes; formation of bromate during ozonation becomes a concern if relatively higher levels of bromide are present in the influent; NDMA is an emerging DBP formed during chloramination and, to a lesser extent, during ozonation. The key to One Water projects, as with conventional projects to a lesser extent, is controlling DBP concentrations to acceptable levels by the design and operation of the treatment methodologies used. Control of DBPs and other carcinogens to meet drinking water standards is now possible and is being demonstrated by several One Water projects. Within the water resource profession, the presence of CECs is considered the "fingerprint" that the water has been impacted by human activity, even if the water and its source appear pristine. CECs include hormones, pharmaceuticals, and personal care products. Obviously, municipal wastewater, being heavily impacted by human activity, contains relatively high concentrations of a wide range of CECs. CEC removal has been possible but expensive. Recent innovations related to the application of the ozone-BAC (ozonation followed by biologically activated carbon) treatment process train are paving the way for cost-effective CEC control and potable reuse across the nation. RO — The Gold Standard Reverse osmosis (RO) is the current "gold standard" for potable reuse of municipal wastewater. RO-based treatment trains have demonstrated removal of pathogens, DBPs, and CECs to drinking water standards. Unfortunately, RO treatment and associated pretreatment steps are expensive to build and operate, and all the removed contaminants are concentrated in a waste stream (sometimes called "reject" or a "brine stream") that is 10 to 20 percent of the influent flow to the RO process. Disposal of this brine stream is another major expense if oceanic Ozone-BAC Technology Influent: Ozone-BAC treatment step is located downstream of the biological secondary treatment. Fully nitrified secondary effluent is the recommended influent for ozone-BAC treatment train. Filtration: Secondary effluent is filtered through a granular medium (sand) or membrane filtration step prior to ozone-BAC treatment train. Ozonation: Oxidation of contaminants is achieved in the ozonation step. Ozone oxidizes and converts slowly biodegradable refractory CECs to readily biodegradable oxidation byproducts. Biological Activated Carbon Filtration: Ozonated effluent is filtered through a BAC bed. It utilizes granular-activated carbon with adsorption capacity as the filter medium. Thus, BAC treatment combines 1) biodegradation to remove CECs and oxidation byproducts, and 2) adsorption to remove CECs that are not amenable for biodegradation. Treated Water: Ozone-BAC effluent is subjected to a final disinfection step prior to water supply augmentation. Figure 2. Ozone-BAC technology description Improvements in advanced wastewater treatment technologies are tilting the economics in favor of the "Single Pipe" approach.

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