Effect of solids retention time on membrane fouling intensity in two-stage submerged anaerobic membrane bioreactors treating palm oil mill effluent.

Submerged anaerobic membrane bioreactors (SAnMBRs) treating palm oil mill effluent were analysed in terms of membrane fouling dynamics when working at three different sludge retention times (SRTs of 15, 30 and 60 d). The average permeate flux was fixed at 2.4 L x m(-2) x h(-1). During operation, the membrane was regenerated by using two steps: membrane wiping during each experiment as soon as trans-membrane pressure reached 125-130 mbars, and complete membrane cleaning including backwash and chemical cleaning at the end of each experiment when analysing the membrane surface and foulant material. Whatever the SRT, the cake formation was the dominant effect on membrane fouling dynamics. The concentration of suspended solids in the SAnMBRs, depending on the SRT, was then a determining criterion. Scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy, Fourier transform infrared spectroscopy indicated that fouled membrane surfaces were covered with a cake layer containing organic and inorganic elements whose concentrations were higher when working at a higher SRT; the higher concentrations of such elements gave to the cake layer a denser and more compact structure. In these experiments, the soluble fractions played a secondary role because of the dominant effect of cake layer structuring.

Performance of constructed wetland treating wastewater from seafood industry.

Wastewater from seafood industry contains high concentrations of organic matter, nitrogen compounds, and solid matter. Constructed wetland can be used as tertiary treatment and for nutrient recycling. This research studied the performance of nitrogen and suspended solids removal efficiency of a constructed wetland treating wastewater from a seafood-processing factory located at Songkhla, southern Thailand. The existing constructed wetland has dimensions of 85 m, 352 m and 1.5 m in width, length and depth respectively, with an area of about 29,920 m2. The water depth of 0.30 m is maintained in operation with plantation of cattails (Typha augustifolia). Flow rate of influent ranged between 500-4,660 m3/d. Average hydraulic retention time in the constructed wetland was about 4.8 days. Influent and effluent from the constructed wetland were collected once a week and analyzed for pH, temperature, dissolved oxygen (DO), biochemical oxygen demand (BOD5), Suspended solid (SS), total Kjeldahl nitrogen (TKN), ammonia nitrogen (NH3-N), organic nitrogen (Org-N), nitrate (NO3-N), and nitrite (NO2-N). The average removal efficiencies of BOD5, SS, TKN, NH3-N, and Org-N were 84%, 94%, 49%, 52% and 82%, respectively. It was found that the constructed wetland acting as a tertiary treatment process provided additional removal of BOD5, SS and TKN from wastewater from the seafood industry.