Water Journal : Water Journal September 2012-1
potable reuse refereed paper technical features 58 SEPTEMBER 2012 water Keywords Drinking water reuse, potable reuse; sustainability; emerging contaminants; triple bottom line; reverse osmosis; granular activated carbon. Abstract The reverse osmosis (RO)-based treatment approach used by some of the newer indirect potable reuse or indirect drinking water reuse (IDWR) plants around the world (e.g., Orange County, CA; Singapore NEWater; Western Corridor, Queensland, Australia) is espoused as a preferred approach, but it is relatively energy intensive and produces a concentrate sidestream that can be difficult and expensive to manage. This provides a challenge, especially for inland locations that do not have access to an ocean discharge. Sustainable management of brine concentrate has become a key factor in the future viability of drinking water reuse for inland locations. Capital cities such as Canberra, Australia, and New Delhi, India, are two examples of inland locations that have or are currently considering IDWR to augment their water supplies. In June 2012, India's first planned drinking water reuse project for New Delhi was launched. Alternative inland IDWR treatment schemes based around granular activated carbon (GAC) are successfully operating at several full-scale facilities in the eastern United States. Both the GAC and RO- based treatment approaches produce excellent finished water quality, but the GAC-based approach has been shown to be significantly less expensive, with lower environmental impacts. Analysis included in this paper shows that both GAC and RO-based treatment trains provide significant reduction of chemicals of emerging concern (CECs), pathogens and bulk organic matter. The capital and operating costs of the GAC- based approach are significantly lower than the RO-based approach and produce less than half of the equivalent greenhouse gas emissions. However, the RO train may be necessary or desirable at those locations that have unacceptable salinity. Approach The purpose of this exercise is to compare the cost, treated water quality, and environmental impact of two full-scale operating treatment systems for indirect drinking water reuse. The following approach was undertaken for this comparison: • Treatment train configuration and finished water quality data were collected from two full-scale GAC- based plants and four full-scale RO-based plants for comparison. Parameters of focus included total organic carbon (TOC), nutrients, pathogens, total dissolved solids (TDS) and CECs. • Actual design criteria and chemical and power consumption data were collected from two full-scale operational indirect drinking water reuse plants -- a 204MLD GAC-based IDWR plant and a 70MLD RO-based IDWR plant. • Using the design criteria collected, construction costs were developed for each treatment train at a normalised flow of 70MLD. Rather than using construction bid data, which is subject to variation caused by the construction date or global and local market conditions, a propriety parametric cost-estimating tool was used to assess the cost of both treatment trains to allow for accurate comparison. • Using the actual chemical and power consumption data collected, annual operating costs were calculated at a normalised average annual flow of 42MLD, which is 60% of the plant's maximum design flow of 70MLD to reflect the lower annual average flows. • The estimated carbon dioxide (CO2) emissions from each treatment train were calculated based on the plant's energy consumption, the energy consumption required for replacement of the plant's major consumables ( e.g., GAC regeneration), and the manufacturing and delivery of chemicals used at the plant. Treatment Provided Figure 1 shows the treatment train provided for the four RO-based IDWR plants evaluated; major treatment processes include fine screening, microfiltration (MF), reverse osmosis, and ultraviolet irradiation or hydrogen peroxide/ultraviolet-based advanced oxidation (AOP). RO concentrate in all cases is discharged to the ocean. High-purity treated water is discharged to a potable water aquifer for three of the four plants analysed; the fourth RO plant discharges to a drinking water reservoir when reservoir levels are low. For the option used in the cost analysis, chemical precipitation is also provided upstream of microfiltration. L Schimmoller, B Angelotti, B Bellamy, J Lozier A case for granular activated carbon based advanced treatment to improve sustainability and reduce cost ACHIEVING DRINKING WATER REUSE WITHOUT REVERSE OSMOSIS SECONDARY EFFLUENT MICROFILTRATION SOLIDS PATHOGENS UVAOP NDMA PATHOGENS CECs REVERSE OSMOSIS NUTRIENTS -- N&P ORGANICS TDS PATHOGENS CECs RO CONCENTRATE -- OCEAN DISPOSAL Aquifer POTABLE WATER CONVENTIONAL WTP FLOC/SED SOLIDS ORGANICS PHOSPHORUS SURFACE WATER RESERVOIR Figure 1. RO-based treatment approach. Secondary Effluent w/ BNR for N Removal LIME CLARIFICATION SOLIDS PATHOGENS PRESSURE FILTRATION SOLIDS PATHOGENS GAC ORGANICS PATHOGENS MICRO - CONSTITUENTS DISINFECTION PATHOGENS SURFACE WATER RESERVOIR CONVENTIONAL WTP POTABLE WATER RECARBONATION CLARIFICATION HEAVY METALS PHOSPHORUS Figure 2. GAC-based treatment approach.
Water Journal November 2012-1
Water Journal August 2012