Sang-Ill Lee

Removal of nitrogen and phosphate from wastewater by addition of bittern

Removal of nitrogen and phosphate through crystallization of struvite (MgNH(4)PO(4).6H(2)O) has gained increasing interest. Since wastewaters tend to be low in magnesium relative to ammonia and phosphates, addition of this mineral is usually required to effect the struvite crystallization process. The present study evaluated the feasibility of using bittern, a byproduct of salt manufacture, as a low-cost source of magnesium ions. High reaction rates were observed; the extent of nitrogen and phosphorus removals did not change beyond 10 min. Phosphorus removals from pure solutions with bittern added were equivalent to those obtained with MgCl(2) or seawater. Nitrogen removals with bittern were somewhat lower than with the alternate Mg(2+) sources, however. Application of bittern to biologically treated wastewater from a swine farm achieved high phosphate removal, but ammonia removals were limited by imbalance in the nitrogen:phosphorus ratio.

Application of struvite precipitation in treating ammonium nitrogen from semiconductor wastewater

Struvite precipitation was applied to the removal of NH(4)-N in semiconductor wastewater. Batch experiments were conducted to examine the effects of final pH, magnesium and orthophosphate dosages and the initial influent concentrations of NH(4)-N and F on the removals of NH(4)-N and PO(4)-P by forming struvite deposits. pH was an important parameter in the simultaneous removals of ammonium nitrogen and orthophosphate. In struvite precipitation, the amount of orthophosphate in the solution affected NH(4)-N removal much more than that of magnesium ions in some cases. It was revealed that the low and high initial concentrations of NH(4)-N and F inhibited NH(4)-N and PO(4)-P removal efficiencies in struvite precipitation, respectively. We also evaluated field-scale treatment plant incorporated by struvite precipitation process. On semiconductor wastewater with an NH(4)-N concentration of 155 mg/L, the results obtained showed that the incorporation of the struvite precipitation process brought about a high NH(4)-N removal efficiency of over 89% on average.

Effect of fermented swine wastes on biological nutrient removal in sequencing batch reactors

Fermented swine waste was compared to acetate for supplementation of bench-scale sequencing batch reactors (SBRs) to improve nutrient removal. Swine waste solids were fermented at room temperature for 10 days. The SBRs were fed diluted swine wastewater and operated on a cycle consisting of the following phases: 10-min anoxic fill, 13-h oxic, 7-h anoxic, 3-h oxic, 40-min settling, 10-min draw. Supplemental organic matter was added at the beginning of the anoxic phase. There was essentially no difference in performance of the reactors supplemented with either acetate or fermented swine waste: both achieved a total nitrogen removal of 90% and a total phosphorus removal of 89%. In comparison, a control reactor (receiving no supplementation) achieved total nitrogen and total phosphorus removals of 76 and 15%, respectively. Sludge phosphorus contents of the supplemented reactors were above 7% of volatile suspended solids, compared to sludge phosphorus content of less than 1% for the control reactor.

Nitrite inhibition of aerobic growth of Acinetobacter sp.

Nitrite inhibition of Acinetobacter sp. growing under aerobic conditions was studied. Specific growth rates under non-limiting concentrations of acetate and dissolved oxygen averaged 0.62h(-1). Growth and phosphate uptake by Acinetobacter sp. were both inhibited by increasing nitrite concentrations. The median inhibitory concentration (IC50) of free nitrous acid (FNA) was 0.10 mg/L and the IC10 of FNA was 0.05 mg/L. Removing nitrite from cultures reversed the inhibitory effect. Comparison of the IC10 of FNA for Acinetobacter sp. to inhibitory concentrations for other wastewater heterotrophic bacteria suggests that Acinetobacter sp. are relatively sensitive to this compound.

Evaluation of struvite obtained from semiconductor wastewater as a fertilizer in cultivating Chinese cabbage.

The present work evaluated the fertilizing value of struvite deposit recovered from semiconductor wastewater in cultivating Chinese cabbage. The fertilizing effect of struvite deposit was compared with that of commercial fertilizers: complex, organic and compost. Laboratory pot test results clearly showed that the growth of Chinese cabbage was better promoted when the struvite deposit was used than with organic and compost fertilizers even though complex fertilizer was the most effective in growing Chinese cabbage. It was revealed that potassium (K) was a key element in the determination of growth rate of Chinese cabbage. Also, the abundant nutrients such as nitrogen (N), phosphorus (P), K, calcium (Ca) and magnesium (Mg) were observed in the vegetable tissue of struvite pot. Specifically, P was the most-founded component in the vegetable tissue of struvite pot. Meanwhile, the utilization of struvite as a fertilizer led to the lowest accumulation of copper (Cu) and no detection of cadmium (Cd), arsenic (As), lead (Pb) and nickel (Ni) in the Chinese cabbage. It was found that the optimum struvite dosage for the cultivation of Chinese cabbage was 1.6 g struvite/kg soil. Based on these findings, it was concluded that the struvite deposits recovered from semiconductor wastewater were effective as a multi-nutrient fertilizer for Chinese cabbage cultivation.

Effect of mixing on spontaneous struvite precipitation from semiconductor wastewater

The objective of this study was to investigate on the effect of mixing intensity (G) and mixing duration (t(d)) on struvite precipitation in the chemical mechanical polishing (CMP) wastewater generated from the semiconductor manufacturing process. Batch-scale experiments revealed that struvite crystallization was affected by both G and t(d). The mixing effect was to enhance the mass transfer of solute to the crystals in the process, resulting in the improvement of struvite crystallization and growth. By forming struvite, removal efficiencies of N and P increased logarithmic with the multiple values of G and t(d), i.e., Gt(d). Insufficient mixing energy with the Gt(d) value less than 10(5) caused an increase in the formation potential of unexpected precipitate unlike to pure struvite, causing a decrease in removal efficiencies of N and P in the process. At the Gt(d) value over 10(6), struvite precipitation was not restricted by fluoride, of which high level inherently contained in the CMP wastewater. The study results can be taken into consideration in the design and operation of the struvite precipitation process for both nutrient (N and P) removal and recovery.

Long term operation of pilot-scale biological nutrient removal process in treating municipal wastewater.

The performance of a pilot-scale biological nutrient removal process has been evaluated for 336 days, receiving the real municipal wastewater with a flowrate of 6.8m(3)/d. The process incorporated an intermittent aeration reactor for enhancing the effluent quality, and a nitrification reactor packed with the porous polyurethane foam media for supporting the attached-growth of microorganism responsible for nitrification. The observation shows that the process enabled a relatively stable and high performance in both organics and nutrient removals. When the SRT was maintained at 12 days, COD, nitrogen, and phosphorus removals averaged as high as 89% at a loading rate of 0.42-3.95 kg COD/m(3)d (corresponding to average influent concentration of 304 mg COD/L), 76% at the loading rate of 0.03-0.27 kg N/m(3)d (with 37.1mg TN/L on average), and 95% at the loading rate of 0.01-0.07 kg TP/m(3)d (with 5.4 mg TP/L on average), respectively.

Microorganisms as efficient biosystem for the synthesis of metal nanoparticles: current scenario and future possibilities

Nanoparticles, the elementary structures of nanotechnology, are important materials for fundamental studies and variety of applications. The different sizes and shapes of these materials exhibit unique physical and chemical properties than their bulk materials. There is a great interest in obtaining well-dispersed, ultrafine, and uniform nanoparticles to delineate and utilize their distinct properties. Nanoparticle synthesis can be achieved through a wide range of materials utilizing a number of methods including physical, chemical, and biological processes with various precursors from liquids and solids. There is a growing need to prepare environmentally friendly nanoparticles that do not produce toxic wastes in their process synthesis protocol. This kind of synthesis can be achieved by green environment benign processes, which happen to be mostly of a biological nature. Microorganisms are one of the most attractive and simple sources for the synthesis of different types of nanoparticles. This review is an attempt to provide the up-to-date information on current status of nanoparticle synthesis by different types of microorganisms such as fungi, yeast, bacteria, cyanobacteria, actinomycete, and algae. The probable biosynthesis mechanism and conditions for size/shape control are described. Various applications of microbially synthesized nanoparticles are summarized. They include antibacterial, antifungal, anticancer, larvicidal, medical imaging, biosensor, and catalytic applications. Finally, limitations and future prospects for specific research are discussed.

Seawater flocculation of emulsified oil and alkaline wastewaters

Abstract Seawater flocculation at high pH was investigated for the removal of emulsified oil and suspended solids from wastewater. As little as 2% seawater by volume, in conjunction with lime or caustic for pH adjustment, was required to achieve good flocculation of the oil-water emulsion. The same amount of seawater allowed efficient removal of suspended solids from alkaline industrial wastewaters and oxidation pond effluent having pH of 10.6 and higher, without addition of an OH − source. Effective flocculation was associated with the precipitation of 2–3.5 g equiv m −3 of Mg 2+ . The minimum seawater concentration for effective flocculation, in relation to pH, was predicted successfully based on the solubility of magnesium in wastewater-seawater mixtures.

Effect of mean velocity gradient and mixing time on particle removal in seawater induced flocculation

Various combinations of mean velocity gradient (G) and mixing time (td) in the seawater flocculation of industrial wastewater and oxidation pond effluent were investigated. The optimum product of these parameters (Gtd) lies within the range of 16,000 to 160,000. Inclusion of a slow mixing phase improved particle removal over that achieved by rapid mixing alone at equal gSGtd. The minimum Gtd at which peak particle removal was achieved decreased as seawater dosage increased. Similar trends were demonstrated with increasing dosages of the flocculant chitosan. An empirical model of flocculation kinetics, having the same form as the partice aggregation-floe breakup model, was found to portray accurately the effects of G and td.