Fort Walton Beach Council agenda — 12-24-2010 Regular — reading text

RO systems create several significant challenges. First, since membranes simply separate various constituents from water, RO creates a " concentrate" stream, typically 15 to 20% of the feed r 0 a water, that contains concentrated levels of the rejected constituents. For example, if the mineral a calcium was in the untreated water at 100 mg /L, it would be treated to nearly 0 mg /L in the Z Z treated stream with a concentration of about 500 mg /L in the concentrate stream that then needs Q to be disposed of. Finding economical methods that will comply with regulatory and public a E perception requirements for reuse or dispose of concentrate can be a challenge. In areas with a suitable geology, deep well disposal is an option. Concentrate cannot be recycled upstream of an Q RO system as the salt concentration very quickly builds to intolerable levels. Concentrate can also be evaporated, dried, and landfilled; however, both the capital and operating costs of drying concentrate are on the order of $3. 00 per 1000 gallons treated more expensive than other disposal methods. Another significant drawback to RO treatment is the high power cost required to operate an RO system. Adding RO to the typical water reclamation plant will increase power consumption for an already energy- intensive system by at least 90 %. Power requirements for RO systems treating reclaimed water range from about 1, 400 to 2, 400 kWh per mgal treated, compared with the Carollo Engineers 7 Packet Pg. 116  14. 1. c average power consumption for existing water reclamation facilities of about 1, 500 kWh/mgal. RO membranes also tend to foul quickly in reclaimed water applications, requiring pretreatment of feed water and regular chemical cleaning of the membranes, both of which increase the cost and complexity of building and operating an RO system. At present most reclaimed water RO systems use microfiltration (MF) for pretreatment. Finally, RO treatment still needs to be preceded by a BNR process. RO alone will not remove ammonia and nitrate to the degree required due to their similar size and molecular characteristics to water. A typical RO membrane will reject about 90% of the nitrate and 95% of the ammonia in the feedwater. While phosphates are better removed by RO membranes ( rejection > 99. 8 %), too much phosphonis going to an RO system will also foul membranes as a result of the precipitation of insoluble phosphate compounds. COSTS TO MEET THE NUMERIC NUTRIENT CRITERIA A Specific Case Study To illustrate the costs to implement additional treatment to meet the proposed numerical nutrient criteria, consider an existing 10 mgd Florida water reclamation plant that meets advanced secondary water quality standards for public access reuse. To meet the numeric nutrient criteria, the biological portion of this plant must be upgraded to meet AWT limits, and then additional tertiary physical -chemical treatment processes must be added. For this example, assume that conventional BNR and MF /RO processes will be used. Based on a study of 50 BNR upgrade projects, the expected cost to upgrade a 10 mgd plant from 0 CL secondary to AWT standards is on average about $ 82 million. Based on bid -data available from a) eleven wastewater treatment plants using MF -RO, adding MF -RO treatment to an existing water Z reclamation plant is estimated to cost between $ 54 million to $ 81 million depending on the Z c concentrate disposal. method. These costs could be significantly higher at existing sites because 0 E of site constraints. The total capital cost to upgrade a 10 -mgd water reclamation facility not s U already meeting AVM /T limits could be in the range of $140 — $160 million, and operating costs Q would increase by at least $ 1. 00 per thousand gallons treated ( about $ 3. 6 million per year), not including concentrate disposal costs which can range from an additional $ 1. 10 per thousand gallons for a deep well up to $ 3. 00 per thousand gallons for a brine concentrator system ( these numbers have been normalized to reflect design flow and not concentrate flow). These additional operating costs are in addition to the estimated $ 1. 00 to $ 1. 50 per thousand gallons being treated already being spent for typical Florida treatment facilities producing water for reuse. Table 3 summarizes the incremental capital costs required to meet the proposed NNC. Carollo Engineers 8 Packet Pg. 117  14.1. c Further, meeting low yearly average nutrient limits requires highly consistent performance by the treatment process, which will likely result in significant conservatism in the sizing of treatment facilities, provision of redundant systems, and other provisions to increase reliability that ultimately add additional costs. These additional costs are not accounted for in the estimates provided here. Table 3 Summary of Incremental Capital Costs ($ M) for BNR and MF /RO Treatment to Upgrade a 10 -mgd Water Reclamation Facility for Three Different Concentrate Disposal Options. Deep Well Deep Well Zero Liquid 3 3 109000 ft) 29500 ft) Discharge Q a BNR Upgrade 80 80 80 W MF -RO Systems' 50 50 50 Disposal2 Concentrate 11 4 a 31 Total 141 134 161 U) 3 cu Notes: J 1. Assumed recoveries: MF = 95 %; RO = 85 %. 2. Concentrate disposal costs are estimated from a combination of bid -data, vendor quotes, and a report published by the c 0 AWWA Membrane Residuals Management Subcommittee. CU 3. Excluding any pretreatment and standby disposal system. 0. 4. With a brine concentrator and brine crystallizer; excluding cost for solids disposal; brine concentrator recovery assumed = 95 %. a 0 The Big Picture 0 In order to further quantify the effect of the proposed NNC on the State, the case study variables 0a described above were applied to all publicly owned wastewater treatment plants documented by a FDEP. The plants were broken down into plants that already have AWT and ones that do not. U Z AWT technology upgrades were assumed and projected to cost $ 8. 20 per design gallon to Z upgrade. Subsequently, all plants would be required to be upgraded by the addition of an a E advanced tertiary technology following AWT. Reverse osmosis was assumed at an average cost of $5. 00 per gallon per day of design treatment capacity. An additional cost of $1. 10 per gallon a of