This study was conducted to examine the production of bioflocculants using agricultural wastewater as a fermentation feedstock under different temperatures and incubation times. The mechanism of flocculation was studied to gain a detailed understanding of the flocculation activity. The highest bioflocculant yield (2.03 g/L) at a temperature of 40 °C was produced in a palm oil mill effluent medium (BioF-POME). Bioflocculant produced from a fermented SME medium (BioF-SME) showed the highest activity. The flocculation tests for colour and turbidity removal from lake water indicated that BioF-SME and BioF-POME performed comparably to commercial alum. Analyses of the bioflocculants using liquid chromatography-mass spectrometry (LC-MS) found that the bioflocculants contained xylose and glucose. The mechanism study showed that flocculation occurred through charge neutralization and interparticle bridging between the bioflocculant polymer and the particles in the lake water. Thus, agricultural wastewater can be used as a fermentation feedstock for high-quality bioflocculants.
In this study, the potential of a pilot-scale granular activated carbon sequencing batch biofilm reactor (GAC-SBBR) for removing chemical oxygen demand (COD), ammoniacal nitrogen (NH3-N) and 2,4-dichlorophenol (2,4-DCP) from recycled paper wastewater was assessed. For this purpose, the response surface methodology (RSM) was employed, using a central composite face-centred design (CCFD), to optimise three of the most important operating variables, i.e., hydraulic retention time (HRT), aeration rate (AR) and influent feed concentration (IFC), in the pilot-scale GAC-SBBR process for recycled paper wastewater treatment. Quadratic models were developed for the response variables, i.e., COD, NH3-N and 2,4-DCP removal, based on the high value (>0.9) of the coefficient of determination (R(2)) obtained from the analysis of variance (ANOVA). The optimal conditions were established at 750 mg COD/L IFC, 3.2 m(3)/min AR and 1 day HRT, corresponding to predicted COD, NH3-N and 2,4-DCP removal percentages of 94.8, 100 and 80.9%, respectively.
A pilot scale granular activated carbon-sequencing batch biofilm reactor with a capacity of 2.2 m3 was operated for over three months to evaluate its performance treating real recycled paper industry wastewater under different operational conditions. In this study, dissolved air floatation (DAF) and clarifier effluents were used as influent sources of the pilot plant. During the course of the study, the reactor was able to biodegrade the contaminants in the incoming recycled paper mill wastewater in terms of chemical oxygen demand (COD), adsorbable organic halides (AOX; specifically 2,4-dichlorophenol (2,4-DCP)) and ammoniacal nitrogen (NH3-N) removal efficiencies at varying hydraulic retention times (HRTs) of 1-3 days, aeration rates (ARs) of 2.1-3.4 m3/min and influent feed concentration of 40-950 mg COD/l. Percentages of COD, 2,4-DCP and NH3-N removals increased with increasing HRT, resulting in more than 90% COD, 2,4-DCP and NH3-N removals at HRT values above two days. Degradation of COD, 2,4-DCP and NH3-N were seriously affected by variation of ARs, which resulted in significant decrease of COD, 2,4-DCP and NH3-N removals by decreasing ARs from 3.4 m3/min to 2.1 m3/min, varying in the ranges of 24-80%, 6-96% and 5-42%, respectively. In comparison to the clarifier effluent, the treatment performance of DAF effluent, containing high COD concentration, resulted in a higher COD removal of 82%. The use of diluted DAF effluent did not improve significantly the COD removal. Higher NH3-N removal efficiency of almost 100% was observed during operation after maintenance shutdown compared to normal operation, even at the same HRT of one day due to the higher dissolved oxygen concentrations (1-7 mg/l), while no significant difference in COD removal efficiency was observed.
The complexity of residual toxic organics from biologically treated effluents of pulp and paper mills is a serious concern. To date, it has been difficult to choose the best treatment technique because each of the available options has advantages and drawbacks. In this study, two different treatment techniques using laboratory-scale aerobic sequencing batch reactors (SBRs) were tested with the same real recycled paper mill effluent to evaluate their treatment efficiencies. Two attached-growth SBRs using granular activated carbon (GAC) with and without additional biomass and a suspended-growth SBR were used in the treatment of real recycled paper mill effluent at a chemical oxygen demand (COD) level in the range of 800-1300 mg/L, a fixed hydraulic retention time of 24 h and a COD:N:P ratio of approximately 100:5:1. The efficiency of this biological treatment process was studied over a 300-day period. The six most important wastewater quality parameters, namely, chemical oxygen demand (COD), turbidity, ammonia (expressed as NH3-N), phosphorus (expressed as PO4(3)-P), colour, and suspended solids (SS), were measured to compare the different treatment techniques. It was determined that these processes were able to almost completely and simultaneously eliminate COD (99%) and turbidity (99%); the removals of NH3-N (90-100%), PO4(3)-P (66-78%), colour (63-91%), and SS (97-99%) were also sufficient. The overall performance results confirmed that an attached-growth SBR system using additional biomass on GAC is a promising configuration for wastewater treatment in terms of performance efficiency and process stability under fluctuations of organic load. Hence, this hybrid system is recommended for the treatment of pulp and paper mill effluents.