2019 CSCE Annual Conference - Laval (Greater Montreal) Conference
Dr. Richard Zytner, School of Engineering, University of Guelph
Dr. Keith Warriner, School of Engineering/U of Guelph
Dr. Ashutosh Singh, School of Engineering/U of Guelph
Reuse of wastewater is a recognized approach to enhance sustainability of resources within a water management program. Literature shows that limited work has been done on the reuse of wastewater from the fruit processing industry (FPI) despite the sector being a heavy water user. One of the challenges is the varied strength and composition of FPI wastewater that ultimatly leads to instability in the membrane bioreactor (MBR) during wastewater treatment and fouling of downstream systems like a reverse osmosis (RO) unit.
The passage of low molecular soluble microbial products (SMP) and extracellular polymeric substances (EPS) components through the MBR membrane system, results in high dissolved organic matter (DOM) loading in the effluent. Operating parameters such as temperature, pH and dissolved oxygen, along with a change in fruit type, promote a shift in the metabolic capacity of the sludge within the reactor leading to a lack of reduction in DOM. Typical analysis of MBR effluent at different dates showed a composition of 5-10 ppm protein, 20-40 ppm carbohydrate and 50-70 ppm humic substances. Correlation with TOC measurement and subsequent standard graphs exhibited more reliable prediction on different EPS components. These products along with unidentified organics foul the downstream RO membrane, making the recycle process difficult. Results showed a 85% flux decline after only 75 h of continuous operation when DOM was 80 ppm. Online membrane management could only improve permeation by 10%, with the flux continuing to decline to about 90% over the next 25 h of operation. Foulant analyses using SEM-EDX and FTIR revealed major inorganic functionality on the surface of the membrane.
Experiments were completed to resolve this critical DOM issue. Various techniques at different scale/doses were investigated using 5 different GAC, 5 different coagulants and 3 coagulant aids. Finally, enhanced coagulation using high dosed alum and ferric chloride coupled with chitosan flocculation was found successful, with substantial reduction in the effluent DOM through liquid phase amorphous adsorption followed by solid phase sorption on the GAC surface. The effluent DOM was reduced to about 6 ppm, achieving a positive 93% reduction. Subsequent bench operations using the pretreated effluent as RO feed showed encouraging results without any flux decline. On-going work is evaluating long-term options for continuous operations that include bio-fouling monitoring, membrane cleaning and performance restoration. The paper will discuss in detail the best management practice (BMP) findings to encourage the sustainable recycling of FPI wastewater.