Membrane distillation with antifouling properties for aquculture effluent treatment
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Date
2019-06
Authors
Nurin Dianah Binti D.M. Premnajeeb
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Abstract
The aquaculture industry is one of the fastest growing agriculture sectors globally. However, its effluent to the environment brings huge impacts to the ecosystem. Membrane Distillation (MD) which is able to purify the effluent offer a promising technology for handling such pollution issues. MD is a thermally-driven separation process, in which only vapor molecules are able to pass through a porous hydrophobic membrane. One of the main limitations of MD for aquaculture application is its susceptible to membrane fouling. In this separation process, the influence of vapor pressure and flow velocity were investigated in the system using treated and untreated fish farm effluent. The increase in feed temperature from 65 ⁰C to 85 ⁰C showed a strong influence on the permeation flux and rejection of nutrients. The highest average flux rate achieved using unfiltered fish farm effluent was at a temperature of 85⁰C with a value of 16.24 L/m2.h. Moreover, the MD process working at a higher feed flow velocity within the range of 6 GPH to 14 GPH also resulted in a higher distilled flux and rejection of nutrients. In this experiment, the highest average flux for unfiltered fish farm was obtained with a value of 12.72 L/m2.h at 14 GPH. The same trend was observed when both experiments was run with distilled water. The membrane was then characterized using scanning electron microscopy (SEM) to further evaluate the fouling and scaling on the membrane surface. After the 60 minutes run, the number of pores on the membrane surface has been reduced. Fouling and scaling leads to blocking of the membrane pores, which reduces the effective membrane area, and therefore the permeate flux obviously decreases. The highest flux was obtained with a feed solution of distilled water, followed by filtered fish farm effluent, unfiltered fish farm effluent and salt water with the values of 15.29, 14.24, 12.59 and 10.68 L/m2.h respectively. This indicated that osmotic pressure is the dominating factor for flux reduction instead of the cake layer fouling.