Blackwater Quality and Filtration
Photo Credit: Stav
Filtration and disinfection of secondary effluent are key to production of tertiary-treated recycled water. Tertiary-treated recycled water is the most common quality of water reclaimed from blackwater, and used in urban, industrial, and agricultural applications. Disinfected tertiary reclaimed water is near the quality of potable water—the difference being extremely low concentration of organic compounds and elevated salt levels.
The persistent organic compounds in filtered effluent—microconstituents—include pharmaceutical and personal care products. When recycled water is used for irrigation, these compounds disintegrate in the soil environment rapidly and are not absorbed in the plant root systems. For potable reuse, additional treatment levels (reverse osmosis membranes, advanced oxidation, etc.) are employed, reducing microconstituent concentrations below detection level.
Centralized and Decentralized Wastewater Treatment
Municipal wastewater treatment systems are nearly all centralized systems, relying on economies of scale and conventional treatment systems. Decentralized treatment and reuse systems are gaining increasing acceptance in various parts of the world, especially where new communities are planned from the ground up and where low-impact development (LID) is embraced. Aside from conventional treatment systems in use in most municipalities, there are emerging treatment systems that rely on natural processes, including constructed wetlands, Living Machine, and other systems relying on biological treatment augmented with minimal physical-chemical intervention. These systems use considerably larger areas of land, but they require much less energy input to achieve similar levels of treatment. Compost toilets, particularly those with urine diverters are another option for decentralized water treatement.