Heavy metal-contained wastewater in China: Discharge, management and treatment.

A large amount of heavy metal-contained wastewater (HMW) was discharged during Chinese industry development, which has caused many environmental problems. This study reviewed discharge, management and treatment of HMW in China through collecting and analyzing data from China's official statistical yearbook, standards, technical specifications, government reports, case reports, and research paper. Results showed that industry wastewater discharged by an amount of about 221.6 × 108 t (in 2012), where emission of heavy metals including Pb, Hg, Cd, Cr(VI), T-Cr was around 388.4 t (in 2012). Heavy metal emission with wastewater in east China and central south China was observed to be graver than that in other areas. However, control of heavy metals in Pb and Cd in northwest China was more difficult compared with other areas. In terms of management, China's government has issued many wastewater discharge standards, strict management policies for controlling HMW discharge in recent years, resulting in reduced HMW discharge. In addition, main HMW treatment technology in China was chemical precipitation, and other technologies such as membrane separation, adsorption, ion exchange, electrochemical and biological methods were also occasionally applied. In the future, chemical industries will be concentrated in northwest China, therefore control of HMW discharge should be paid much more attention in those areas. In addition, more effective and environment-friendly heavy metal removal and regeneration technologies should be developed, such as biomaterials adsorbent.

Enhanced ammonia nitrogen removal using consistent ammonium exchange of modified zeolite and biological regeneration in a sequencing batch reactor process.

Utilizing preferential ion exchange of the modified zeolite, the zeo-sequencing batch reactor (SBR) is recommended for a new nitrogen removal process. In this study, natural zeolite was modified by sodium chloride to enhance sorption capacity for ammoniacal nitrogen. The untreated and treated zeolite was characterized by XPS and XRD techniques. The sorption isotherm tests showed that equilibrium sorption data were better represented by the Langmuir model than by the Freundlich model. Treatment of natural zeolite by sodium chloride increased the sorption capacity for ammoniacal nitrogen removal from aqueous solutions. As a result of the continuous bioregeneration of ammonium saturated zeolite-floc in the SBR, the nitrogen removal efficiency of the zeo-SBR was relatively ideal. Scanning electron microscopy results showed that microbes were abundant in the zeo-SBR process.

Characterization and adsorption mechanism of Zn2+ removal by PVA/EDTA resin in polluted water.

Batch adsorption experiments were conducted using a PVA/EDTA resin as an adsorbent to adsorb Zn(II) ions from single component system in which experimental parameters were studied including solution pH, contact time, adsorbent dose and initial metal ions concentration. The equilibrium isotherms were determined at pH 6 under constant ionic strength and at different temperatures. The results showed that the maximum removal of Zn(II) (99.8%) with 1 g L(-1) of sorbent was observed at 40 mg L(-1) at an initial pH value of 6. Removals of about 60-70% occurred in 15 min, and equilibrium was attained at around 30 min. The equilibrium data for the adsorption of Zn(II) on PVA/EDTA resin was tested with various adsorption isotherm models among which three models were found to be suitable for the Zn(II) adsorption. In addition, the kinetic adsorption fitted well to the pseudo-second-order model and the corresponding rate constants were obtained. Thermodynamic aspects of the adsorption process were also investigated. Furthermore a higher desorption efficiency of Zn(II) from the PVA/EDTA resin using acid treatment was available by more than 95%.

[Aerobic granulation for dimethyl phthalate biodegradation in a sequencing batch reactor].

This study investigated the feasibility of aerobic granulation for dimethyl phthalate (DMP) with the glucose as co-metabolism substrate in a sequencing batch reactor (SBR). Experimental results showed that aerobic granulation could be successfully realized in the reactor by controlling the organic loading and sludge settling time. The system could achieve average removal efficiencies of 92.3% for DMP and 90.6% for COD after 75 days operation. The DMP intermediate metabolites were determined and identified as monomethyl phthalate and phthalic acid. Degradation kinetics was well described by substrate inhibition pattern as Haldane equation, and the corresponding kinetic coefficients of V(max), K(s) and K(i) were 643.2 mg x (g x h)(-1), 171.0 mg x L(-1) and 337.5 mg x L(-1), respectively. Environmental scanning electronic microscope (ESEM) results showed that a clearly defined boundary with high porosity on the coarse surface. Many filamentous, coccoid and rod-shape bacteria were visible on the external surface of the granules.

Immobilization of nanoscale Fe0 in and on PVA microspheres for nitrobenzene reduction.

In this study, nanoscale Fe(0) was immobilized in and on poly(vinyl alcohol) (PVA) microspheres by the inverse suspension crosslinked method. Two different sizes of Fe(0)/PVA microspheres were synthesized in the presence and absence of dispersant. The chelating action between Fe(2+) and PVA was identified by Fourier transform infrared and X-ray photoelectron spectroscopy. The morphology and distribution of the obtained Fe(0)/PVA microspheres were characterized by environmental scanning electron microscope, energy-dispersive X-ray spectrometry, and X-ray diffraction. Nanoscale Fe(0) particles were mostly dispersed over the surface of the microspheres. They were distributed more homogeneously on the surfaces of Fe(0)/PVA microspheres with diameter of 600-700 microm than those with diameter of 10-12 microm. The nitrobenzene (NB) reduction reactions followed pseudo-first-order kinetics. The normalized surface rate constants (k(SA)) values were determined to be 0.162 L h(-1)m(-2) for L-Fe(0)/PVA microspheres, 0.098 L h(-1)m(-2) for S-Fe(0)/PVA microspheres, and 0.023 L h(-1)m(-2) for nanoscale Fe(0) particles. Furthermore, with the analysis of the products by GC/MS, possible reductive pathways of NB by Fe(0)/PVA microspheres were suggested. The recovery rates of iron in microspheres were determined to be 81.17% for large Fe(0)/PVA and 60.31% for small Fe(0)/PVA.

[Effect of temperature on the Pb2+ biosorption with aerobic granules].

Experimental studies were conducted on the effect of temperature on the Pb2+ biosorption with aerobic granules seeding with floccular activated sludge. The results showed that the aerobic granules manly comprised the elements of C, H, N, O and P. According to the elemental compositions of the microbial granules, the corresponding empirical formula of the granules can be determined as C5.7 H10.9 O3.9 NS0.04. ESEM results showed many coccoid bacteria were visiable on the granule surface with porous structure. Both Freundlich and Langmuir isotherm equations could describe the biosorption process well (R2 > 0.914)under various temperature (20-40 degrees C). The maximum biosorption capacity (Q(max)) increased from 80.65 mg x g(-1) (20 degrees C) to 97.09 mg x g(-1) (40 degrees C). The values of thermodynamic parameters (deltaG < 0, deltaH > 0, deltaS > 0) indicated the biosorption process was spontaneous and endothermic in nature. Moreover, the Fourier transform infrared spectroscopy (FTIR) results demonstrated that such active groups as -OH, -COOH and P = O were involved in Pb2+ biosorption but nothing to do with nitrogen-containing groups.

Removal of Cr3+ from aqueous solution by biosorption with aerobic granules.

Aerobic granules were utilized as an effective biosorbent to remove Cr(3+) from aqueous solution. The results showed that the initial pH, contact time, and Cr(3+) concentration affected the biosorption process significantly. Both Freundlich and Langmuir isotherms were able to describe the equilibrium data reasonably with high correlation coefficients (R(2)>0.95) and pseudo-second-order model best fitted the biosorption process at experimental conditions. Moreover, Environmental Scanning Electronic microscope (ESEM), X-ray energy dispersion (EDX), and Fourier transform infrared (FTIR) analyses revealed that metal complexation, chemical precipitation, and ion exchange were involved in the removal of Cr(3+) with aerobic granules. Further analysis by a metal ion fraction test demonstrated that metal complexation could be the dominant mechanism of biosorption, whereas chemical precipitation and ion exchange appeared only to have minor role in the overall Cr(3+) biosorption process.

[Treatment of micro-polluted river water by immobilized microorganism technique].

The effect of immobilized microorganism technique on the micro-polluted river water was studied by four kinds of gaia-biological aerated filter (G-BAF), which were formed by special microorganism (BP35) and four different carriers, including haydite, FPUFS, aquamats flexible carrier and artificial aquatic mat. The removal rates of NH4(+) -N, chlorophyll and turbidity were 83.0%-89.0%, 77.5%-89.0% and 84.4%-95.2%, respectively, and they were all higher than the removal rates of COD, UV254 and TP. The FPUFS contained reactive groups, such as hydroxyl, epoxy and acylamide groups, which made FPUFS load a great amount of enzymes and microorganisms. Therefore, the removal rates of pollutants for FPUFS-G-BAF were higher than those for the other three kinds of G-BAF. Hydraulic retention time (HRT) had little effect on the removal rate of NH4(+) -N, while affected the removal rate of COD significantly. When the concentration of dissolved oxygen (DO) increased from < 2 mg/L to > 4 mg/L, for the four kinds of G-BAF, the removal rates of COD and NH4(+) -N increased 11.9%-18.0% and 12.7%-16.1%, respectively. The result of GC-MS showed that the technique of G-BAF could effectively degrade the macro-molecule refractory organics into small-molecule substance.

[Effect of salinity on immobilized microorganisms in biological aerated filter (BAF)].

Based on the satisfactory treatment effect of synthesized oil field wastewater with salinity of 0 - 3%, the salinity effect on the immobilized microorganism in the biological aerated filter (BAF) was further investigated. It was shown that the quantity of live microorganisms could rise to 1.3 x 10(7) per cm3 as the influent salinity was less than 1%, whereas it would decline to 1.1 x 10(6) per cm3 as the salinity increased to 2%, accompanied with the small and cracked cells running out in effluent in the domesticated system. Dehydrogenase activity (DHA) was the highest of 14.4 microg/(mg h) at salinity of 0.5%, which means the greatest degradation capability. And the extra cellular polysaccharide (ECP,) excreted by microorganisms to immobilize themselves on the carriers was the most of 209.9 microg/mg at the salinity of 2%. Although extra cellular polymers (ECP(s)) and microorganisms weight accumulated during the react system operation, the macro-pore diameter of patented FPUFS was from 0.3 to 0.7 mm, which could avoid the clog caused by the microorganisms and their ECP(s), and retained agreeable air and water condition for microorganisms under high salinity.

[Study on treatment of coking wastewater by A/O process of biological filter].

Coking wastewater was treated by A/O process of biological filter with a special kind of carrier. The wastewater contained much more phenolic compounds with about 2000 mg/L of COD and 260 mg/L of NH4+ -N. The A/O system could achieve average removal efficiencies of 87.0% and 91.6% for COD and NH4+ -N, respectively, when HRT was 60 h. The NH4+ -N in the effluent could meet the first level of National Discharge Standard at optimal operation condition. The phenolic compounds with low molecular weight could be fully biodegraded by A/O system. The organic compounds in the effluent were in the relative molecular weight range of 10,000-30,000 and contained --OH, C==O, C--O and phenyl group. Based on the support and protection of the carrier, a great number of microorganisms adhered and immobilized on the outer and inner surface of carrier, which contributed to a simultaneous removal of COD, NH4+ -N and TN. The A/O system biological filter showed a characteristic of steady performance and resistance ability during the operation period.

[Biodegradation of oil field wastewater in biological aerated filter (BAF) by immobilization].

A special kind of carrier was used to immobilize effective microorganisms B350M in a biological aerated filter (BAF) react system for treatment of oil field wastewater, which is of salinity > 0.5%, lack of N and P, and contains low organic matter. Through the biodegradation system operated for 142d, the react system can achieve average degradation efficiency 90.5%, 74.4%, 85.6%, 100% for oil, TOC, COD and H2S, when HRT was 4h and COD volumetric load was 1.07 kg/(m3 x d). GC-MS results show that the organic substance in wastewater contain 27 different kind substances, a majority (23) of alkane and a minority (4) of aromatic substances. C14H30 to C28H58 in influent could be decomposed into small molecular substance efficiently, especially the C18H38 to C28H58, and also polycyclic aromatic hydrocarbons (PAHs) such as Phenanthrene. The react system had a good diversity, because the carriers provide agreeable air and water condition for microorganisms, to resist high salinity and toxic pollutant. Filamentous microorganisms were observed in a great deal and will not cause foaming and bulking in BAF reactor by immobilization.