The US National Research Council recently recommended direct potable water reuse (DPR), or potable water reuse without environmental buffer, for consideration to address US water demand. However, conveyance of wastewater and water to and from centralized treatment plants consumes on average four times the energy of treatment in the USA, and centralized DPR would further require upgradient distribution of treated water. Therefore, information on the cost of unit treatment processes potentially useful for DPR versus system capacity was reviewed, converted to constant 2012 US dollars, and synthesized in this work. A logarithmic variant of the Williams Law cost function was found applicable over orders of magnitude of system capacity, for the subject processes: activated sludge, membrane bioreactor, coagulation/flocculation, reverse osmosis, ultrafiltration, peroxone and granular activated carbon. Results are demonstrated versus 10 DPR case studies. Because economies of scale found for capital equipment are counterbalanced by distribution/collection network costs, further study of the optimal scale of distributed DPR systems is suggested.

Biological removal of dichloromethane (DCM) from pharmaceutical industry is limited by its recalcitrance. In this study, an airlift packing reactor (ALPR), which combined the suspended and fixed-film microbial growth system, was set up to remove DCM and co-existed toluene. The removal performance of the ALPR for DCM was greater than traditional airlift reactor (ALR). The maximum elimination capacity (EC_max) of the ALPR for DCM reached 108 g m^-3 h^-1 with removal efficiency (RE) of 41%, increased by 145% if compared to the ALR. The EC_max for toluene was 172 g m^-3 h^-1 with RE of 70%, decreased by 25% if compared to the ALR, which was mainly due to the higher liquid-phase biomass in the ALR. The results of high-throughput sequencing showed that the microbial composition on the packings of the ALPR had a large difference from its liquid-phase or the liquid-phase of the ALR. Gemmobacter, Rhizomicrobium, Chitinophaga, Vampirovibrio, and Fodinicurvata were genera with great abundance fixed on the packings and Rhizomicrobium, Chitinophaga, Vampirovibrio, and Fodinicurvata are first to be reported in VOCs biological removal. This study indicated that the ALPR can augment the microbial community and effectively improve the removal of recalcitrant VOCs.

Net-zero water (NZW) is a new vision for municipal water management, in which significant water is neither imported to, nor exported from the service area, i.e. local water independence. While such a system has long been possible in areas of sufficient water supply and/or sparse population, it is now becoming possible and economical for municipal systems in virtually any modern watershed, through the use of emerging direct potable reuse (DPR) technology. In fact, current implementations are producing design and operating data. Moreover, distributed NZW systems recycling at a high rate are projected to be capable of energy-positive operation, saving more domestic hot water energy than is consumed in treatment. However, NZW and DPR approaches vary widely in terms of source water, source segregation, treatment, and recycling rate. In this study, a workshop was convened to assemble and synthesize a broad cross-section of current NZW and DPR experience, to develop recommendations for water management planning. It was concluded that technology is currently emerging to support widespread NZW management. Recommendations included the introduction of NZW systems into new construction, to be supported by controlled demonstration projects over periods of two years or more; development of supporting regulatory structure with public engagement; development of real-time water quality monitoring devices; and retention of the term “net-zero water” to signify a new water management vision to advance water and energy autonomy.