Process Study, the Development and application of Novel Low-Fouling Membranes for Fish Processing Wastewater Treatment through Membrane Bioreactor (MBR) Technology

Abstract

Management of wastewater from industries is a challenge in many urban centers in developing countries due to scarcity of space as lagoons and maturation ponds (with large footprint) are largely used for wastewater treatment. A typical example is Kisumu City, a major fish source to the Kenya economy and a host of fish processing companies. The sewerage system coverage in the city is poor with most of the industries lacking proper connection. The fish processing industries are intensive consumers of high volumes of clean water and later release huge amounts of wastewater (effluent) on daily basis. Most of these industries lack proper wastewater treatment facilities and discharge effluent on open drainage systems. The huge investiment required to construct proper wastewater treatment facilities is a challenge that fish industries have to overcome. In view of the high land prices and scarcity of space in urban centers, the need to install wastewater treatment facilities that are cost effective, efficient and of low footprint has been realized. In the present work, application of membrane bioreactor (MBR) technology for treatment of fish processing wastewater in fish industries was studied. The study investigated the efficiency of commercial polyethersulfone (PES) membrane, the development and application of novel low-fouling membrane for treatment of fish processing wastewater through MBR Technology. The physicochemical parameters of fish processing wastewater were determined. Process optimization for the performance of commercial UF/PES membrane modules was done at a laboratory scale in JKUAT using the immersed membrane bioreactor (iMBR) unit. A novel low fouling membrane was developed through surface modification of commercial PES membrane via the polymerizable bicontinuous microemulsion (PBM) technique. Tests for the fouling characteristics of commercial UF/PES membrane and PBM-coated membrane were done using the automated cross-flow testing cell and the lab-scale MBR unit. The cost-benefit for a containerized MBR system was determined. The studied UF/PES membrane modules showed good performance for water permeability during pilot testing but were found to be susceptible to fouling. A novel low-fouling membrane was successfully developed through a successful coating process. This was demonstrated using IR spectrums that confirmed the presence of PBM coating and, by the low contact angle (CA) of 31.6±2.2˚-34.1±2.8˚ thus indicating that hydrophilic property was achieved for the modified membrane. The PBM-coated module showed improved ability to resist fouling with no critical flux achieved at TMP of up to 340mbar relative to the PES module whose critical flux was observed at 7.3L/m2*h with TMP of 230mbar. PBM module had higher removal efficiency for COD, (NO3--N and NH4+-N) and PO43--P in the range of 96±1%, 88±1%, and 84±1% in comparison to 92±2%, 80±3%,and 64±1% for the PES module respectively with mean values significantly different (tobserved ˃ tcritical) for paired T-test (at 95 % confidence level). The MBR system had a cost benefit of 82.8% per m3 of treated water. The correlation cost curves demonstrated that, small-scale MBR systems with a volume flow of 10m3/d to 30m3/d are cost-effective in terms of capital expenditure (CAPEX) in comparison to activated sludge process (ASP) systems, where investment cost is driven higher by the cost of land and site redesign requirements. However, MBR systems have high operation expenditure (OPEX) due to the high energy requirements. Nonetheless, MBR systems encourage the reuse of high-quality treated water (for washing, irrigation etc.) which makes them economical during the course of the plant life. In conclusion, the analysis showed that small-scale MBR containerized systems could become an economic solution for small industries, (such as fish processing industries) in the urban centers in Kenya, where land scarcity and high costs are a major challenge.