No abstract

Most seafood wastewater has been treated by the activated sludge process. Due to changes in salt concentration, pollutant loadings and raw materials, the process is not operated satisfactorily to meet effluent regulation. Most problems faced at present are solid liquid separation. In this study, effects of salt concentration on floc characteristics and pollutants removal efficiencies were investigated in treatment of seafood wastewater by SBR. For analyzing fractal dimension of flocs, the small angle laser light scattering (SALLS) method was applied using a Diffraction Particle Sizer (Malvern Instruments). Organic removal efficiencies (in terms of COD(Mn)) decreased with increasing salt concentration, but eventually reached a steady state. Fractal dimension and floc size also showed similar trends with changing salt concentration. The main reasons to reduced pollutant removal efficiencies were deteriorated biological activity and settling properties. The biological activity was affected faster than the floc characteristics by increasing salt concentration. The deteriorated settling properties were explained by decreased size and fractal dimension of floc due to increasing salt concentration. The settling properties of floc such as sludge volume index (SVI) and zone settling velocity (ZSV) were related to size and fractal dimension of floc. The fractal dimension of floc was better related to the settling properties than the size of floc.

This paper investigates the characteristics of graphene oxide (GO) for Bisphenol A (BPA) adsorption in water. Batch experiments on the influence of significant parameters were performed. While an improvement of the adsorption capacity of BPA was obtained by the increment of contact time and the initial BPA concentration, the increment of pH above 8, GO dosage, and temperature showed the reverse results. The thermodynamic study suggested that BPA adsorption on GO was an exothermic and spontaneous process. The kinetics was explained by the pseudo-second-order model which covers all steps of adsorption. The fit of the results with the Langmuir isotherm indicated the monolayer adsorption. At 298 K, the adsorption reached equilibrium within 30 min with the maximum adsorption capacity of 49.26 mg/g. The low BPA adsorption capacity of GO can be interpreted by the occurrence of oxygen-containing functional groups (OCFGs) that are able to form hydrogen bonds with the surrounding OCFGs and water molecules. This effect inhibited the role of π–π interactions that are mainly responsible for the adsorption of BPA.

A non-woven fabric filter was experimentally evaluated for solid-liquid separation in an activated sludge reactor as an alternative membrane. A polypropylene fabric filter (70, 50 and 35 g/m2) was used for the experiment. The pilot system was operated in A/O (Anaerobic/Oxic) type in which the filter module was submerged into the oxic compartment. The filtration module consists of 10 plate type rectangular filter elements with effective filtration area, 2 m2. Gravity filtration was carried out for solid-liquid separation by changing the water head 0.05-0.5 m without backwashing during the system operation. Initial permeate flux was set at 0.4 m/d. C/N ratio of raw wastewater was controlled at 4.5 in terms of BOD/T-N. The fabric filter system showed a good performance enough for domestic wastewater treatment. Effluent solid concentration was 3.2 mg/L (93.5% removal). COD removal efficiency was 91.6% producing an effluent concentration around 13 mg/L. 66% of total nitrogen removal could be obtained at the adjusted C/N ratio of influent wastewater. However phosphorus removal was very low at 23%. It was found that the initial flux of 0.4 m/d should be maintained for stable performance of the system.

The sorption characteristic of biological powdered activated carbon (BPAC) were investigated in a hybrid membrane process which was accomplished by introducing powdered activated carbon (PAC) into a crossflow microfiltration system and seeding microorganisms. This combined process was designated BPAC-MF and could be an alternative system for reclamation of secondary sewage effluent. Experiments were carried out to identify the ability of BPAC to remove various dissolved refractory organic matter in secondary sewage effluents such as peptone, beef extract, lauryl sulfate, humic acid, tannin, lignin and gum arabic. Adsorption test by fresh powdered activated carbon (PAC) showed significantly different adsorption characteristics for each organic substance. These adsorption characteristics were identified by the analysis of gel permeable chromatography (GPC). The sorptive capacity of BPAC was almost four times higher than that of fresh PAC. This phenomenon could be explained from the sorption capacity of PAC and BPAC for each substance. For the hardly adsorbable refractory organics, humic acid and gum arabic, the sorption capacity of bPAC was 12.1 and 8.7 mg/g respectively. These values are significantly high compared with 3.6 and 0.2 mg/g obtained by PAC. It was estimated that the enhanced sorption capacity of BPAC was due to the stimulation of activated carbon adsorption by biological effect.