Polishing Treatment of Molasses Wastewater with Iron Salts: the Role of Counter-ions

The effect of counter-ions on the coagulation of biologically treated molasses wastewater using iron-based coagulants was investigated. Parameters such as removals of chemical oxygen demand (COD) and color, and residual turbidity, were measured to evaluate coagulation performance. Experimental results showed that ferric chloride and ferric nitrate were more effective than ferric sulfate at optimal dosages, achieving 89 to 90% and 98 to 99% of COD and color removals, respectively, with residual turbidity of less than 5 NTU. High-performance size exclusion chromatography (HPSEC) results revealed differences in the removal of the molecular weight fraction of organic compounds using iron salts. Scanning electron microscopy (SEM) showed randomly formed coagulated flocs characterized with irregular, sheet-like shapes. Nitrate and chloride counter-ions had similar effects on coagulation performance compared to sulfate. Both FeCl3 and Fe(NO3)(3) yielded better results than Fe(SO4)(2) under underdosed and optimum dosage conditions. Coagulation efficiency was less adversely affected in the overdosed regions, however, if sulfate rather than chloride or nitrate was present. Water Environ. Res., 81, 2293 (2009).

Variables affecting melanoidins removal from molasses wastewater by coagulation/flocculation

Coagulation/flocculation process was applied in the polishing treatment of molasses wastewater on a bench-scale. Important operating variables, including coagulant type and dosage, solution pH, rapid mixing conditions as well as the type and dosage of polyeletrolytes were investigated based on the maximum removal efficiencies of chemical oxygen demand (COD) and color, residual turbidity and settling characteristics of flocs. HPSEC was utilized to evaluate the removal of molecular weight fractions of melanoidins-dominated organic compounds. Experimental results indicate that ferric chloride was the most effective among the conventional coagulants, achieving 89% COD and 98% color eliminations; while aluminum sulfate was the least effective, giving COD and color reductions of 66% and 86%, respectively. In addition to metal cations, counter-ions exert significant influence on the coagulation performance since Cl--based metal salts attained better removal efficiency than SO42--based ones at the optimal coagulant dosages. Coagulation of molasses effluent is a highly pH-dependent process, with better removal efficiency achieved at lower pH levels. Rapid mixing intensity, rather than rapid mixing time, has relatively strong influence on the settling characteristics of flocs formed. Lowering mixing intensity resulted in increasing settling rate but the accumulation of floating flocs. When used as coagulant aids, synthetic polyelectrolytes showed little effects on the improvement in organic removal. On the other hand, cationic polyacrylamide was observed to substantially enhance the settleability of flocs as compared to anionic polyacrylamide. The effects of rapid mixing conditions and polymer flocculants on the coagulation performance were discussed. (C) 2009 Elsevier B.V. All rights reserved.

In situ nutrient removal from aquaculture wastewater by aquatic vegetable Ipomoea aquatica on floating beds

Nutrient-rich effluents caused rising concern due to eutrophication of aquatic environment by utilization of a large amount of formula feed. Nutrient removal and water quality were investigated by planting aquatic vegetable on artificial beds in 36-m(2) concrete fishponds. After treatment of 120 days, 30.6% of total nitrogen (TN) and 18.2% of total phosphorus (TP) were removed from the total input nutrients by 6-m(2) aquatic vegetable Ipomoea aquatica. The concentrations of TN, TP, chemical oxygen demand (COD) and chlorophyll a in planted ponds were significantly lower than those in non-planted ponds (P<0.05). Transparency of water in planted ponds was much higher than that of control ponds. No significant differences in the concentration of total ammonia nitrogen (TAN), nitrate nitrogen (NO3-N) and nitrite nitrogen (NO2--N) were found between planted and non-planted ponds. These results suggested that planting aquatic vegetable with one-sixth covered area of the fishponds could efficiently remove nutrient and improve water quality.

Effects of thiamine on treatment performance of textile wastewater

Textile wastewater is commonly treated with activated sludge process technology. However, its treatment performance has not been demonstrated to be very effective. In this study, the effects of micronutrient thiamine on removal efficiencies of dissolved organic carbon (DOC) and chemical oxygen demand (COD) of textile wastewater in a batch test, together with its effect on the oxygen uptake rate (OUR) of activated sludge, were evaluated. Significant improvements were observed in the removal rates of DOC, COD and OUR with 121%, 156% and 121% of those of the control, respectively, when 0.5-2.0 mg/L thiamine was added to the wastewater treatment system. Thiamine could be probably used to improve the treatment performance of textile wastewater.

Bacterial diversity in activated sludge from a consecutively aerated submerged membrane bioreactor treating domestic wastewater

The bacterial diversity of activated sludge from submerged membrane bioreactor (SMBR) was investigated. A 16S rDNA clone library was generated, and 150 clones were screened using restriction fragment length polymorphism (RFLP). Of the screened clones, almost full-length 16S rDNA sequences of 64 clones were sequenced. Phylogenetic tree was constructed with a database containing clone sequences from this study and bacterial rDNA sequences from NCB1 for identification purposes. The 90.6% of the clones were affiliated with the two phyla Bacteroidetes (50%) and Proteobacteria (40%), and beta-, -gamma-, and delta-Proteobacteria accounted for 7.8%, 28.1%, and 4.7%, respectively. Minor portions were affiliated with the Actinobacteria and Firmicutes (both 3.1%). Only 6 out of 64 16S rDNA sequences exhibited similarities of more than 97% to classified bacterial species, which indicated that a substantial fraction of the clone sequences were derived from unknown taxa. Rarefaction analysis of operational taxonomic units (orrUs) clusters demonstrated that 150 clones screened were still insufficient to describe the whole bacterial diversity. Measurement of water quality parameter demonstrated that performance of the SMBR maintained high level, and the SMBR system remained stable during this study.

Effects of micronutrients on biological treatment efficiency of textile wastewater

Micronutrients play a very important role in biological processes for wastewater treatment. Many industrial wastewaters lack in nutrients (macronutrients and micronutrients) required for microbial growth, and this is one of the main problems at many activated sludge plants treating industrial wastewater. The microbial community structure is one of the important factors controlling the pollutant-degrading capacity of biological wastewater treatment system. In this study, the concentrations of micronutrients of the textile wastewater discharged from a textile plant were determined, and the effects of micronutrients on treatment efficiency and microorganism community structure of the biological treatment system were studied. The results showed that the optimal concentrations of magnesium, molybdenum, zinc, thiamine and niacin in the textile wastewater were 5.0, 2.0, 1.0, 1.0 and 1.0mg/L, respectively. The COD removal rates when magnesium, molybdenum, zinc, thiamine and niacin were added individually to the wastewater in their optimal concentrations were 1.8, 1.4, 1.3, 1.6 and 2.2 times of that of the control, respectively. The improving effects of combinations of zinc and thiamine, zinc and niacin, thiamine and niacin were better than single micronutrient. The diversity of quinones (DQ) changed significantly after the micronutrient was added into the wastewater treatment system. This indicated that there was probably a feasibility of optimizing the biological treatment performances and microorganism community structure of textile wastewater treatment system through micronutrient supplement.

Micronutrient niacin addition to enhance biological treatment of textile wastewater

Micronutrients play an important role in biological processes for wastewater treatment. Many industrial wastewaters lack in nutrients required for microbial growth, and this is one of the problems at many activated sludge plants treating them. In this study, the effects of the micronutrient niacin on the COD removal rates of textile wastewater, together with the effect of Mixed Liquor Suspended Solids (MLSS) on niacin, were studied. Certain improvement effects were found on the removal rates of COD, when 0.5 similar to 2.0 mg/L niacin was added to the textile wastewater. The optimal concentration of niacin was 1.0 mg/L, which was continuously added during textile wastewater treatment, and removal rates were 1.31 times compared to those of the control system. The concentration of MLSS was probably one of the factors influencing treatment efficiency, and the biological performance of treatment system could be optimized through micronutrient niacin supplements.

Discharges and sediments as sources of extracellular alkaline phosphatase in a shallow Chinese eutrophic lake

Total alkaline phosphatase activity (APA) and soluble reactive phosphorus (SRP) concentrations were measured in municipal wastewater, and a shallow Chinese freshwater lake receiving it. Activities of Dissolved alkaline phosphatase ( ADAP) in overlying and interstitial water were also analyzed monthly at three sites for several years. The lake was enriched with SRP and alkaline phosphatase by discharge of the wastewater, indicating that the inclusion of APA for estimating water pollution was reasonable. Annual data showed that APA in coarser fraction was significantly higher at the site receiving more wastewaters, both in surface and overlying water, suggesting that resuspension of enzyme most likely occurred in the basin heavily discharged. ADAP was an order of magnitude higher in the wastewater than those in lake waters, and was generally higher in interstitial water, a feature more striking at the site receiving more discharges. Besides, it was irrespectively inhibited by Na2WO4, L-cysteine and EDTA-Na, but stimulated by Cu2+, Zn2+, CTAB and Triton X-100 in interstitial, overlying and surface waters. This similarity of responding patterns to the stressors indicated an analogy between dissolved alkaline phosphatase in water column and that in interstitial water, supporting the hypothesis that the polluted sediments act as source of dissolved alkaline phosphatase in eutrophic lakes.

Removal of dibutyl phthalate by a staged, vertical-flow constructed wetland

Two sets of small scale systems of staged, vertical-flow constructed wetlands (VFCW) were operated in a greenhouse to study the purification of dibutyl phthalate (DBP) in admeasured water. Each system consisted of two chambers in which water flowed downward in chamber I and then upward in chamber 2. The systems were intermittently fed with wastewater under a hydraulic load of 420 mm(.)d(-1). The measured influent concentrations of DBP in the experimental system were 9.84 mg(.)l(-1), while the other system was used as a control and received no DBP. Effluent concentrations of the treated system averaged 5.82 mug(.)l(-1) and were far below the Chinese DBP discharge standard of less than or equal to0.2 mg(.)l(-1). These results indicate the potential purification capacity of this new kind of constructed wetland in removing DBP from a polluted water body.

Roles of substrate microorganisms and urease activities in wastewater purification in a constructed wetland system

A vertical/reverse-vertical flow constructed wetland system was set up in Wuhan, China, to study its treatment efficiency of polluted lake water. The numbers of substrate microorganisms and urease activities in the substrate of the constructed wetland were determined by plate counts and colorimetric analysis, respectively. The removal efficiencies of biochemical oxygen demands (BOD5). chemical oxygen demands (COD), total phosphorus (TP), total Kjeldahl nitrogen (TKN), and total suspended solids (TSS) were measured by EPA approved methodology. The results showed there were significant positive correlations (P < 0.05) between numbers of microorganism in the substrate and removal rates of TKN and CODCr. Meanwhile, there was significant positive correlation (P < 0.05) between urease activities and removal efficiencies of TKN and negative correlation between urease activities and removal efficiencies of BOD5. Substrate microorganisms and urease activities played key factors during purification processes and they could be utilized as indicator of wastewater treatment performances in the constructed wetland system. (C) 2004 Elsevier B.V. All rights reserved.

The role of plants in channel-dyke and field irrigation systems for domestic wastewater treatment in an integrated eco-engineering system

Eight kinds of plants were tested in channel-dyke and field irrigation systems. The removal rates of TP, phosphate, TN, ammonia, CODcr and BOD, in the channel-dyke system with napiergrass (Pennisetum purpurem Schumach, x Pennisetum alopecuroides (L.) Spreng American) were 83.2, 82.3, 76.3, 96.2, 73.5 and 85.8%, respectively. The field irrigation systems with rice I-yuanyou No.1(88-132) (Oryza sativa L.) and rice II- suakoko8 (Oryza glaberrima) had high efficiency for N removal; the removal rate were 84.7 and 84.3%, respectively. The mass balance data revealed that napiergrass, rice I and II were the most important nutrient sinks, assimilating more than 50% of TP and TN. Plant uptake of N and P as percentage of total removal from wastewater correlated with biomass yield of and planting mode. (C) 2000 Elsevier Science B.V. All rights reserved.