Water Reuse for Food Processing in Canada — Case Study

Introduction A potato processor in Canada treats wastewater generated on-site for direct discharge to a surface water body via an on-site wastewater treatment plant (WWTP) that includes anaerobic digestion and a membrane bioreactor (MBR). The MBR effluent directed for discharge was evaluated to potentially reuse back in the potato processing facility after tertiary treatment. The analysis included the following elements: 1) Review and identification of information provided by the Canadian Food Inspection Agency (CFIA) and guidelines for Canadian drinking water quality (GCDWQ) that may impact water reuse for food production and impact on system design, verification, and validation. 2) Mass balance to evaluate capital costs, system operation, precipitation potential, and antiscalant and cleaning chemicals required to achieve suitable water recovery from high-pressure membrane tertiary treatment. 3) Return on investment and selection of water reuse objective. The case study explores the uncertainty in the regulatory environment for water reuse projects in Canada in the food and beverage sector. The objective of the project was to understand the risks to water reuse on-site and costs associated with the design and operation of a water reuse treatment system that maximizes water reuse for economical capital and operating costs, balance precipitation product formation and chemical dosing costs, compliance with the existing discharge permit, maximize water reuse and water reduction targets, and meet outcome-based water quality objectives to maintain food safety. Basis of Design The existing effluent discharged off-site was evaluated against the parameters in the GCDWQ to develop concentration based performance targets for the water reuse treatment system (WRTS), before review and analysis of pathogen loading and removal. The objective of the WRTS and review against the GCDWQ was to align where practical with the GCDWQ without necessarily meeting the full requirements of the potable water quality standards. The potato processor utilized ultrafiltration (UF) polyvinylidene fluoride (PVDF) hollow fiber membranes that achieved excellent water quality, as exemplified by the silt density index (Table 1) and comparison to the GCDWQ where the filtrate exceeded ammonia-nitrogen, E. coli, total coliforms, conductivity, cryptosporidium, giardia, manganese, pH, N-nitrosodimethylamine-d6, sulfate, total dissolved solids, and temperature. The selected system to complete treatment focused on a high-pressure membrane treatment system and residual chlorine dosing system. Water Projections Geosyntec evaluated the performance of a high-pressure membrane treatment system and projected permeate and effluent quality. The effluent quality projected to be discharged off-site was estimated by combining effluent not directed to the WRTS and the concentrate stream generated by the high-pressure membrane system. To balance the impact of concentrating ionic species on membrane performance and discharge water quality, Geosyntec evaluated two scenarios: 1) Scenario 1 — recirculation of high-pressure membrane concentrate back to the on-site WWTP for additional removal across the process. 2) Scenario 2 — Blending of high-pressure membrane concentrate with effluent not directed to the WRTS. After the analysis was completed, the preferred scenario included blending a portion of high-pressure membrane concentration to the on-site WWTP and effluent stream. The water quality projections for the influent to the WRTS in two scenarios for evaluating high-pressure membrane systems that are provided in Table 2. The precipitation products and chemical dosing required to maintain membrane performance were analyzed in incorporated into the economic analysis. The result of the analysis indicated the following outcomes were feasible and economical for the WRTS: 1) 75% reduction in water purchased by the facility. 2) 60% to 75% recovery across the high-pressure membrane. 3) Compliance with the existing discharge permit. Food Safety and System Operation Geosyntec evaluated the food safety and outcome-based approach for system design and operation. The units of operation and monitoring of the WRTS selected are summarized below: 1) Flow equalization. 2) Continuous turbidity and monthly monitoring reporting. 3) Continuous membrane integrity monitoring (conductivity and transmembrane pressure) to divert off-specification reuse water and collect other data ongoing to verify system operation. 4) WRTS effluent residual chlorine dosing and continuous residual chlorine monitoring. 5) Validation period during challenge testing conditions, estimated to be summer and fall months for potato processing when the oldest potatoes from potato sheds (summer) are entering production and when fresh potatoes are harvested off the fields for production (fall) 6) Validation study of system performance and operation. 7) Verification process by third-party. Process Design The design criteria and food safety components were used to solicit vendor proposals for high-pressure membrane treatment systems and informed the balance of the process design of the treatment system, summarized in the process flow diagram (Figure 1) for the WRTS relative and WWTP flow streams. The vendor bids, equipment costs, and validation and verification period were used for consideration to advance the design of the WRTS.