Case Study on ETP Performance Improvement in Primary and RO Pretreatment in a Plastic Recycling Unit

BackgroundPlastic recycling processes typically begin with washing and cleaning the plastic materials to prepare them for further processing. This cleaning step generates wastewater that may contain a variety of contaminants, including plastic particles, residual chemicals, cleaning agents, dyes, and additives used during manufacturing..The feed water for this system originates from a plastic bottle recycling plant, with treated water intended for reuse in the process after it meets the desired quality parameters. As a result, wastewater from plastic recycling must undergo adequate treatment before being discharged into the environment or reused. Improper disposal or inadequate treatment of this wastewater can have serious environmental consequences, harming aquatic ecosystems and freshwater resources. Contaminants in wastewater can harm aquatic life and may enter the food chain, posing risks to human health..System DetailsTreatment sequence includes equalization → pH increase → Coagulation & Flocculation in secondary clarifier → PSF → ACF → UV → UF → Reuse in plant..Wastewater from recycling units typically contains prominent levels of pollutants, including TDS, TSS, oil and grease, and fillers. The standard treatment procedure involves using inorganic coagulants or cationic polymeric coagulants to remove colloidal impurities and break oily emulsions..Conventional Coagulant (Liquid PAC 1000 ppm) effective only at Alkaline pH i.e. raised by Spent Caustic & Anionic flocculant 0.5 ppm. pH adjustment posts primary treatment by Spent Acid. .Chembond’s team developed a customized coagulant specifically designed to target these impurities without altering the final discharge pH or increasing the solid load in the system, ensuring efficient treatment while maintaining system stability.Issue IdentificationThe Chembond’s team has been treating the plant effluent successfully for a considerable period, maintaining consistent treatment performance.The conventional treatment approach (i.e., Alum + Anionic Flocculant) was no longer effective in breaking the tight emulsions and colloidal impurities.After primary treatment, the effluent appeared milky white and hazy due to emulsified oils, which is difficult to remove using the commodity coagulants..When this tight emulsion/turbid effluent reached the secondary treatment system, there was no significant reduction in COD and BOD, and the supernatant remained turbid at the secondary clarifier outlet..Additionally, thick sludge and scum accumulated on the clarifier surface. The clarifier scraper, designed to remove such sludge, failed due to a design flaw, resulting in ineffective scum removal..Consequently, the tertiary system experienced increased load, impacting the RO system. This led to more frequent CIP cycles and a reduction in the final treated water output, which is essential for production.• Increase in TDS across primary treatment due to the addition of spent caustic and spent acid for pH correction• Low permeate flow, operating at less than 15% of the designed capacity• Increased feed pressure (>15%) impacting membrane performance• Frequent CIP requirement, approximately once per week.SolutionFollowing unsatisfactory results with conventional coagulants, our team introduced a Chembond polymeric coagulant blend at the primary clarifier inlet, combined with an anionic flocculant. This reduced COD from 3000 ppm to 800 ppm at the primary outlet and to 200 ppm at the secondary outlet, resulting in a clear supernatant..In primary treatment, liquid PAC was replaced with Chembond polymeric coagulant and an anionic flocculant without increasing pH, eliminating the need for spent caustic and spent acid, and reducing TDS at the primary outlet..To control foaming from surfactant load, a silicone-based defoamer was replaced with a 100% degradable, non- silicone antifoaming agent suitable for RO membranes..In tertiary treatment (RO pretreatment), alum/PAC was replaced with a low-cationic, degradable polymeric coagulant combined with an anionic flocculant. This eliminated alumina and excess cationic charge at UF and RO inlets, delivering excellent performance and maintaining SDI below 2 at the recommended dosage..Case Study – Recycling UnitKey Issues Identified:· High COD levels at inlet: 2186.5 mg/L· Poor COD reduction: Only 55.5% in Primary· Elevated TDS in RO reject: 972.7 mg/L· High suspended solids: TSS 515.6 mg/L.Case Study – Recycling UnitResultsThe addition of the specialized KEMFIX coagulant to the system yielded extremely positive results in reducing COD and TSS.Within just 5 days of introducing the polymer into the clarifier, its effect was clear: existing surface deposits were removed, and no new scum formed on the lamella clarifier surface. The images below clearly illustrate the before-and-after condition of the clarifier following the use of KEMFIX Coagulant.Key Operational Results Observed:Increased RO Recovery: RO permeate increased to 400 M3/Day compared to earlier 250 M3/DayDue to increased Feed Pressure within 5 to 6 days only, CIP needed to be carried out every week, the frequency drastically reduced to 45 days compared to earlier every 7 daysImproved RO permeate Quality and SDI maintained 1-2, only than earlier 4 to 5Reduction in sludge formation due to high dose of Caustic, PAC and Acid.High alumina content has fouled membrane, eliminated by replacing Alum.COD load to RO feed observed around 250 ppm & may contributed Organic fouling further led to increased Feed pressure with reduction in permeate flow.Improvement in RO feed and Permeate flow. After elimination of PAC in tertiary clarifier drastic reductionin sludge generation additional caustic or lime required to neutralize the pH as KEMFIX coagulant does not make any difference in treated effluent ph. Clarifier outlet parameters such as TSS maintained consistently below 20 ppm. Turbidity below 1 NTU and SDI after UF maintained below 2.. Water Chemistry – With Chembond Treatment Key Improvements Achieved:· COD inlet reduced by 90.8%: 2186.5 → 200.9 mg/L.· Primary efficiency improved to 72.8%· RO reject TDS reduced by 51.8%: 972.7 → 468.5 mg/L.· TSS inlet reduced by 76.1%: 515.6 → 123.1 mg/L..ConclusionChembond’s customized KEMFIX coagulant performed exceptionally well in primary clarification, it is microorganism-friendly and does not generate dead mass in aeration tanks during biological treatment. Additionally, replacing PAC with KEMFIX Coagulant improved water clarity and consistently reduced turbidity, maintaining SDI below 3.With strong and consistent support from Chembond Water Technologies, the challenges related to primary discharge and RO pretreatment were successfully addressed, resulting in consistent improvements in effluent quality.