IN THE FIELD
in dry seasons and reduced the consumption of tap water in the petrochemical process. The reclaimed water can prolong the regeneration time of ion exchange resins in the pure water process, reducing the production of reclaimed wastewater and reaching a virtuous cycle of in-plant water usage through reclaimed water. Another petroleum refinery in southern Taiwan was also introduced to MBR of ultrafiltration (UF) level as a RO pretreatment unit for wastewater reclamation. The main difference was that the original activated sludge biological treatment unit was rebuilt into part of a MBR facility, and the existing sedimentation and sand filtration units were not in operation as this plant had a lack of space and a relatively mature MBR+RO technology. This wastewater treatment capacity was 8,000m 3 /day, and the amount of reclaimed water was over 5,600m 3 /day. After the performance test, the reclaimed water featured conductivity of less than 100μs/cm from 2,500-4,500μs/cm, with nearly a complete removal of COD from 100mg/L to 550mg/L, and the amount of sulphate to less than 10mg/L from over 1,000mg/L. After the MBR+RO treatment process, the petroleum refinery wastewater treated for discharge turned into reclaimed water, serving as an alternative in dry seasons and improving the quality of the plant’s existing tap water resources. The third case was also in a petrochemical plant in southern Taiwan. Although the wastewater from this plant had a high amount of conductivity, there was high percentage of chloride. Furthermore, the WRP needed to have 80% of water resources from reclaimed water. EDR was set up as the main process, which was suitable for addressing water with a high amount of hardness and chloride. Submerged membrane filtration (SMF) was also set up for pretreatment, and RO was for post-treatment to increase the supply flexibility and stability of different levels of reclaimed water for temporary storage and transportation. Since the EDR could be regarded as the pretreatment unit of the RO, substances of water were first treated through EDR,
Over the past 10 years, CTCI has carried out industrial wastewater reclamation using MBRs or EDR combined with RO technology (Image: CTCI)
increasing the recovery rate of RO to more than 85%. Originally, the wastewater from this petrochemical plant could only be discharged after treatment. By using this hybrid of multimembrane process of SMF-EDR-RO, 3,000m 3 /day of wastewater could be reclaimed back to petrochemical process for reuse, equivalent to reducing the same amount of tap water usage and wastewater discharge to neighbouring environment. There is also a greater demand for water resources in high-tech industries related to electronics semiconductors. In recent years, CTCI took part in a construction WRP project under a design, build, own and operation (DBOO) agreement in southern Taiwan, which would serve as a new water resource in the science and industrial park. The capacity of this WRP is 20,000m 3 /day during phase one, and is expected to reach 30,000-36,000m 3 /day. Effluents are pumped from the wastewater treatment plant (WWTP) as raw materials, which are monitored by an online analyser of key water quality before entering the WRP. This is followed by a two-stage biological treatment unit where pollutants such as total organic carbon (TOC) and ammonia nitrogen in the water would be removed via the nitrification of microorganisms. The contact aeration biological treatment process is used, which prolonged the retention time of microorganisms and pollutants so as to increase the removal efficiency of TOC and ammonia nitrogen, as well as reduce the amount of biological sludge that needs to be discarded due to microbial proliferation.
Fluidised crystallisation bed is also chosen as it reduces the volume of waste sludge and it complements with the traditional coagulation-flocculation-sedimentation softening unit. This stabilises the function of the softening unit. After softening, the water is filtered by low-pressure continuous backwash sand filter and the UF unit is used to remove debris in the water. In order to remove remaining pollutants such as TOC and boron in the water to parts per billion (ppb) concentration level, the two-pass and two-stage RO membrane unit are used. The residual urea in the water will then be treated through chemical reaction to ppb level. The treated wastewater will now be qualified to being reused in the semiconductor manufacturing processes. Before entering the system of reclaimed water supply, the product water quality such as pH, conductivity, turbidity, urea, boron, and ammonia nitrogen will be monitored by the online analyser of the monitoring tank. If the water quality reaches warning level, the control system will automatically switch the mode of water supply to the re-processing mode, ensuring that the water quality of the final product always meets the standard of the end customer. The WRP is also designed to achieve environmental protection and energy conservation by using over 70% of invertor motor-driven rotatory machinery. It also has solar panels on the roof of the buildings to generate electricity — which not only provides electricity for plant-operation, but also connects to the power grid of ‘Taipower’ to sell electricity — achieving the operational goal of energy conservation and environmental protection.
Water & Wastewater Asia | September-October 2024 33
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