Volume 13, Issue 1 - Ontario Onsite Wastewater Association

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13 th Annual Onsite Wastewater Conference & Exhibition Innovative Approaches for Surface Discharge of Treated Effluent from Decentralized Wastewater Treatment Systems Roger Lacasse, Scientific and Technical Director, Premier Tech Aqua, lacr@premiertech.com Naider Fanfan, Project Engineer, Premier Tech Aqua, fanp@premiertech.com Abstract: Where decentralized wastewater treatment is concerned, cost-effective phosphorus removal (DP) and disinfection (DI) processes represent major challenges that are, phosphorus removal without a pH exceeding a discharge limit of 9.5 and reliable disinfection processes with no intensive maintenance requirements. Over the past three years, Premier Tech Aqua has tested various approaches to integrate DP and DI options into decentralized wastewater treatment systems for flow rates ranging from 500 to 50,000 GPD. First, a system that combined an electrocoagulation process and an absorbent media-based filter was tested over a one-year period. This system reduced total phosphorus to below 0.3 mg/L and fecal coliforms to below 200 counts/100 mL. Second, a wastewater disinfection approach based on self-cleaning UV systems was successfully tested under real-life conditions on several different sites. Finally, by combining an innovative chemical addition system with a membrane technology (MBR), a very high level of phosphorus removal was attained (total phosphorus below 0.1mg/L). Introduction: The challenges associated with the surface discharge of treated effluent from wastewater treatment systems are many. The quality of the treated effluent must meet discharge criteria established to protect the receiving environment and also depending on how the water will be used (drinking water, human contact, etc.). A global evaluation of a watershed, as relates to water quality, water usage and protection of specific sensitive environments, makes it possible to establish discharge criteria for the different lakes and rivers of the watershed. Discharge criteria often require low concentrations in TSS, BOD5, phosphorus, bacteria, turbidity, ammonia, etc. All these targeted parameters have an impact on the quality of the receiving water. Phosphorus discharge is an emerging concern because of its direct impact on the lake eutrophication process (blue algae problem). Ensuring disinfection of wastewater without generating by-products (e.g., trihalomethanes from chlorination) is of prime importance to protect the health of the population (U.S. EPA. 1999). Material and methods: The first approach, based on a self-cleaning electro-coagulation process for phosphorus removal and disinfection, was extensively tested over a one-year period on a testing platform located in Rivière-du-Loup (Canada). The tested system consisted of a 1,250gallon primary treatment tank equipped with an outlet flow-control device that regulated the flow rate to 25-30 gallons per hour and fed the selfcleaning electro-coagulation unit (EC) followed by an absorbent media-based filter (Ecoflo® Biofilter with a 70 ft² filter bed). The EC unit was installed in a 500-gallon tank divided into two compartments: a reaction compartment equipped with two pairs of electrodes (aluminium plates) and a propeller unit that provided a high level of turbulence around the electrodes, followed by a second compartment in which a lamellar structure provided for the separation of suspended solids. The EC electrodes were electrically fed by a 48 VDC generator, assuring constant-intensity current, and a pump 22
13 th Annual Onsite Wastewater Conference & Exhibition located under the lamellar separator that, once a day, transferred sludge produced by the EC unit to the primary reactor. Domestic wastewater was fed into the system at a flow rate of 400 GPD by applying the NSF 40 dosing protocol: 25% of the daily volume (Qd) from 6 a.m. to 9 a.m., 35% of Qd from 11 a.m. to 2 p.m., and 40% from 5 p.m. to 8 p.m. Sampling over 24hour periods was done every 2 weeks. The second approach involved a self-cleaning UV disinfection unit used to disinfect secondary level treated effluent. The self-cleaning UV unit consisted of a central quartz tube that received the effluent to be treated and in which stainless steel blades rotated to clean the quartz tube 6 times a day to overcome quartz tube fouling (Sehnaoui,K. and Gehr, R. 2001). Two UV lamps were installed on each side of the central quartz tube, with a parabolic reflector to maximize UV radiation (Patented Crossfire Technology®). This disinfection unit was extensively tested at two (2) different sites. In both cases, the wastewater treatment unit included a septic tank followed by an equalization tank and a rotating biological contactor in front of the self-cleaning UV unit. The UV unit was fed by a pump at a regulated flow rate of 15 GPM. The first system was used to service a new subdivision of 100 homes, producing a design flow rate of 27,000 GPD. Sampling at this site was done for 24 months. The second system treated the wastewater produced by a restaurant at a flow rate of 4,000 GPD. Its performance was evaluated over a period of 36 months. The third approach was based on a membrane biological reactor (MBR) that produced a tertiary level treatment, including very low Table 1 Average concentrations (± standard deviation) for EC unit and absorbent filter system concentrations of total phosphorus, by adding a chemical coagulant to the treatment line. The pilot system was installed at a commercial site (office building) equipped with an existing wastewater treatment system that treated an average flow rate of 6,600 GPD. The MBR pilot unit included two ultra-filtration modules (14 m² of membrane each) based on flat sheet membranes that received septic tank effluent from the existing system at an average flow rate of 900 GPD. A chemical used for phosphorus removal was fed from the equalization tank effluent to the septic tank inlet on a recirculation loop. Results and discussion: The results obtained with the first system (an EC unit combined with an absorbent media-based filter) are presented at Table 1. As shown, the EC unit removed total phosphorus to below 1.0 mg/L. Addition of an absorbent media-based filter, after the EC unit, reduces the total phosphorus to 0.1 mg/L and all other parameters (TSS, BOD5, fecal coliforms, and turbidity) below tertiary level treatment. The high quality of the treated effluent meets the usual criteria for surface discharge in sensitive areas. As described previously, the self-cleaning UV disinfection unit was extensively tested at two (2) different sites. In both cases, the selfcleaning UV unit was installed at the effluent of a secondary treatment system. The performances at the first site, which treated the wastewater from a 100-home subdivision, are presented in Tables 2 and 3. Disinfection near detection level was obtained on a constant basis. Parameter Units Raw wastewater Septic tank effluent EC effluent Filterv effluent n TSS mg/L 176 ± 45 124 ± 71 38 ± 10 1.2 ± 1.8 (0.8) 23 BOD5 mg/L 195 ± 22 150 ± 51 112 ± 20 2.5 ± 0.6 (2.5) 22 Total P mg/L 9.1 ± 0.8 5.7 ± 1.6 0.6 ± 0.2 0.1 ± 0.04 (0.1) 23 Fecal coliforms (1) counts/ 715,000 408,000 5,300 67 63 Turbidity 100 mL 106 ± 41 142 ± 43 59 ± 25 0.6 ± 0.1 21 pH NTU 7.3 ± 0.1 6.9 ± 0.1 7.6 ± 0.2 6.9 ± 0.1 21 Table 2 Average concentrations at the influent of the self-cleaning UV unit (100-home subdivision) Parameter Units Average Median Min. Max. n TSS mg/L 14 ± 8 14 3 31 25 BOD5 mg/L 7 ± 3 6 3 17 25 Fecal coliforms counts/100 mL 1,695 (1) 3,100 30 12,000 11 UV transmissivity % 59 ± 3 59 56 67 10 (1) Geometric average Table 3 Average concentrations at the effluent of the self-cleaning UV unit (100-home subdivision) Parameter Units Average Median Min. Max. n Fecal coliforms counts/100 mL 11 (1) (1) Geometric average 10 2 100 33 Tables 4 and 5 present the performance of the self-cleaning UV unit installed at the restaurant site. Again, the results obtained indicate disinfection below detection level under all conditions tested. Table 4 Average concentrations at the influent of the self- cleaning UV unit (restaurant) Parameter Units Average Median Min. Max. n TSS mg/L 21 ± 9 20 8 45 45 BOD5 mg/L 9 ± 6 8 2 30 48 Fecal coliforms counts/100 mL 823 (1) 800 230 5,300 22 UV transmissivit % 60 ± 14 57 37 92 25 (1) Geometric average Continued on page 32 … 23
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Volume 13, Issue 1 - Ontario Onsite Wastewater Association

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