Review of cost versus scale: water and wastewater treatment and reuse processes

Abstract

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.

Modeling the Economic Feasibility of Large‐Scale Net‐Zero Water Management: A Case Study

“…Capital and operation and maintenance (O&M) costs are estimated based on previously published cost functions (Guo et al, 2014); conveyance energy computed based on potential and kinetic energies, friction losses, and required water line gauge pressure; pipeline installation costs; and Fourier's Law estimates of energy savings based on retention of wastewater thermal energy. Total unit water costs are then found by amortizing capital over a 30-year planning period, summing costs in constant 2012 U.S. dollars, and subtracting the cost of energy saved because of retention of wastewater thermal energy in the treated water.…”

“…Before running the model, the cost functions for wastewater treatment unit processes embedded in the model (Guo and Englehardt, 2015;Guo et al, 2014) were used to estimate the capital cost of the proposed new WDWWTP and compared with the current cost estimate obtained by the county for verification of the cost functions as possible for application in the Miami-Dade County study area. The county proposes to construct an 153-mgd MBR plant to treat normal municipal wastewater flow, with a parallel aeration and ballasted high-rate flocculation process to be activated to address peak wet-weather flows of up to 62 mgd.…”

“…Because this conveyance energy is reportedly 4 times the energy of treatment, DPR and NZW may offer an energy advantage over dual-conveyance reclamation systems for irrigation. However, the only known true public water supply NZW implementation currently is the International Space Station in that other DPR implementations recycle less than 50% of wastewater, hence drawing the majority of source water from environmental sources such as reservoirs (Carter, 2009;Englehardt et al, 2013;Guo et al, 2014). In contrast, a research NZW system that recycles 85 to 90% of commingled domestic wastewater is currently being demonstrated at a university residence hall (Englehardt et al, 2013).…”

“…In fact, DPR has been recommended, in general, to address increasing water demand and the replacement of aging water/wastewater infrastructure (Englehardt et al, 2013;NRC, 2011;Tchobanoglous et al, 2011). While the cost of DPR technology remains less certain than those of conventional systems, generalized costs of unit processes that may be used in DPR systems were recently reviewed, updated, and demonstrated as a function of system scale (Guo et al, 2014). In addition, an optimization model was presented to provide generalized principles regarding the scaling of distributed DPR NZW systems to optimize the balance between economy of scale in terms of capital cost and diseconomy of scale in terms of water conveyance energy and costs (Guo and Englehardt, 2015).…”

The Environmental Biorefinery: Using Microalgae to Remediate Wastewater, a Win-Win Paradigm

“…The demand for freshwater and industrial nutrients can be significantly reduced, thus bringing down the production cost and environmental impact of the whole process. Additionally, the cost of wastewater treatment using conventional processes can be as high as 0.682 $/m 3 if membrane bioreactors are used [12]. Part or of this cost can be recuperated in the form of credits for the positive environmental impact created by wastewater remediation by microalgae.…”