Chihpin Huang

Adsorption of Cu(II) and Ni(II) by pelletized biopolymer

Chitosan and Ca-alginate, derivatives of biopolymer, were separately prepared from crab chitin and algin in pellet form for adsorption of Cu(II) and Ni(II) from aqueous solutions. The capability of these biopolymers was also investigated to remove copper and nickel from aqueous solutions in an immobilization system, along with a comparison made of these biopolymers with other adsorbents. Additionally, the feasibility of alginate/chitosan in pellets to remove nickel ion and nickel cyanide complex from polluted water was investigated. Stabilizing chitosan physically in an alginate support medium was deemed possible, by means of which both free metal and metal cyanide ions could be removed from aqueous solutions in an engineering system. However, the crosslinking reaction during immobilization would result in blocking of some adsorption sites.

Application of Aspergillus oryze and Rhizopus oryzae for Cu(II) removal

Biosorption of copper(II) by the untreated and acid-treated fungal biomass has been studied in both batch and column modes. Two species, Aspergillus oryzae and Rhizopus oryzae, were used in this study. A. oryzae mycelia (undergoing acid-washing) exhibit a clear advantage in Cu(II) removal, compared with other adsorbents. The acid-washing process can strongly enhance the adsorption capacity for A. oryzae mycelia. However, acid-washing does not alter the metal adsorption capacity of R. oryzae mycelia. The result indicates that acid-washing is not only a pretreatment step but also a regeneration step in the heavy metal removal process. These dual purposes, therefore, give the acid-washing biomass an indication of successful prospect. Cultivating A. oryzae in pellet form is an effective means of mycelium immobilization. The method established in this study provides the high-yield, uniformly-sized particles (2–3 mm in diameter), which are effective in solid-liquid separation. This pellet column can completely remove metals before breakpoint. After the breakpoint, a significant amount of Cu(II) removal over a long period has been observed. This is thought to be the result of intracellular uptake.

Application of nanosilver surface modification to RO membrane and spacer for mitigating biofouling in seawater desalination

Biofouling is one the most critical problems in seawater desalination plants and science has not yet found effective ways to control it. Silver compounds and ions are historically recognized for their effective antimicrobial activity. Nanosilver particles have been applied as a biocide in many aspects of disinfection, including healthcare products and water treatment. This study proposes an innovative biofouling control approach by surface modification of the RO membrane and spacer with nanosilver coating. A chemical reduction method was used for directly coating nanosilver particles on the membrane sheet and spacer. The surface-modified membrane and spacer were tested for their antifouling performance in a cross-flow flat-sheet membrane cell, which is a part of a pilot plant in Wukan desalination plant. The silver-coating membranes and spacers, along with an unmodified membrane sheet, were tested in the membrane cell and compared on the basis of their antifouling performance. Permeate flux decline and salt rejection was continuously monitored through the testing period. Meanwhile regrowth of microbial populations on the membrane cell was quantified by a unique microbial counting every three to four days. The results showed that both silver-coated membrane (Ag-cM) with uncoated spacer and silver-coated spacer (Ag-cS) with uncoated membrane performed better than the unmodified membrane and spacer (Un-MS), in terms of much slower decrease in permeate flux and TDS rejection. However, the effect of silver-coated spacer on antimicrobial activity was more lasting. In the silver-coated spacer test, there was almost no multiplication of cells detected on the membrane during the whole testing period. Besides, the cells adhering to the membrane seemed to lose their activity quickly. According to the RO performance and microbial growth morphology, the nanosilver coating technology is valuable for use in biofouling control in seawater desalination.

Application of a supported iron oxyhydroxide catalyst in oxidation of benzoic acid by hydrogen peroxide

Oxidation of benzoic acid was studied via Fenton-like reaction using an innovative supported γ-FeOOH catalyst. The decomposition kinetics of hydrogen peroxide was investigated first. Oxidation of benzoic acid by hydrogen peroxide was performed to understand the effects of initial pH and hydrogen peroxide dosage. The treatment efficiency of benzoic acid at an initial pH of 3.2 was higher than at initial pHs of 6.0 and 10.0; this can be partly explained by reductive dissolution of γ-FeOOH. Therefore, the extent of heterogeneous catalysis was evaluated. We found that the majority of oxidation occurred on the catalyst surface, with some occurred in the solution due to iron dissolution of the catalyst.

Operation optimization of Thiobacillus thioparus CH11 biofilter for hydrogen sulfide removal

Abstract Members of the autotrophic species, Thiobacillus thioparus CH11, were isolated from swine wastewater and immobilized with Ca-alginate to produce pellet packing materials for a novel biofilter system that controls hydrogen sulfide emission. The effect of operating parameters, including retention time, temperature, and inlet gas concentration, on the removal efficiency and capacity was evaluated. Criteria necessary for a scale-up design of the biofilter were established and the sulfur balances at various loadings were tabulated. High and satisfactory H2S removal efficiency levels were maintained during operation and the optimal retention time was found to be 28 s corresponding to a H2S removal efficiency greater than 98%. The pH drop was insignificant in this biofilter. The optimal inlet S-loading can be noted as 25 g m−3 h−1 that is at the upper end of linear correlation between inlet loading and removal capacity. We suggest that the Thiobacillus thioparus CH11 immobilized with Ca-alginate is a potent method to control hydrogen sulfide emissions.

Biological elimination of H2S and NH3 from wastegases by biofilter packed with immobilized heterotrophic bacteria

Biotreatment of various ratios of H2S and NH3 gas mixtures was studied using the biofilters, packed with co-immobilized cells (Arthrobacter oxydans CH8 for NH3 and Pseudomonas putida CH11 for H2S). Extensive tests to determine removal characteristics, removal efficiency, removal kinetics, and pressure drops of the biofilters were performed. To estimate the largest allowable inlet concentration, a prediction model was also employed. Greater than 95%, and 90% removal efficiencies were observed for NH3 and H2S, respectively, irrespective of the ratios of H2S and NH3 gas mixtures. The results showed that H2S removal of the biofilter was significantly affected by high inlet concentrations of H2S and NH3. As high H2S concentration was an inhibitory substrate for the growth of heterotrophic sulfur-oxidizing bacteria, the activity of H2S oxidation was thus inhibited. In the case of high NH3 concentration, the poor H2S removal efficiency might be attributed to the acidification of the biofilter. The phenomenon was caused by acidic metabolite accumulation of NH3. Through kinetic analysis, the presence of NH3 did not hinder the NH3 removal, but a high H2S concentration would result in low removal efficiency. Conversely, H2S of adequate concentrations would favor the removal of incoming NH3. The results also indicated that maximum inlet concentrations (model-estimated) agreed well with the experimental values for space velocities of 50-150 h(-1). Hence, the results would be used as the guideline for the design and operation of biofilters.

Optimal condition for modification of chitosan: a biopolymer for coagulation of colloidal particles

Chitosan, an acetylated derivative of chitin, is a biodegradable cationic polymer. Chitosan can be a promising substitute for alum in the coagulation process, because of its potential feasibility in coagulation without posing any health threat as the residual aluminium and other synthetic polymers do. In this study, various pretreatment conditions were tested in search of the optimum chitosan modification. Batch tests with synthetic source water suggest that the optimal pretreatment condition to prepare modified chitosan coagulant is deacetylation by 45% alkali solution for 60 min, followed by dissolution in 0.1% hydrochloric acid.

Coagulation of colloidal particles in water by chitosan

The feasibility of applying chitosan, as prepared from the crab chitin, was assessed in this study for the coagulation of colloidal particles. A series of batch flocculation tests with chitosan under different conditions was also conducted. The results indicate that chitosan is a potent coagulant for bentonite suspension. The relationship between the optimum chitosan dosage and the turbidity of the bentonite suspension is presented as a linear correlation. The evidence infers that an adequate range of the coagulant dosage is the primary consideration in determining the removal efficiency for the turbidity of the source water. It also indicates that the coagulation behavior for kaolinite by chitosan is different from that of bentonite, i.e., chitosan fails to form a good aggregate with kaolinite. Turbid water containing particles which show behavior similar to kaolinite apparently need to have some bentonite particles added as coagulant aid, thereby improving the aggregation of the colloid particles with chitosan. Moreover, the effect of pH on the coagulation efficiency of chitosan is insignificant. The evidence infers that charge neutralization is not a major mechanism controlling the formation of floc for chitosan coagulation.

Coagulation dynamics of fractal flocs induced by enmeshment and electrostatic patch mechanisms

The size and structure of flocs during floc formation were monitored for various coagulation mechanisms. Two distinctive mechanisms, namely, enmeshment and electrostatic patch, govern the dynamics of kaolin particles coagulation by polyaluminum chloride (PACl). They were investigated by small angle static light scattering (SASLS) and solid-state (27)Al NMR. In addition, a novel wet SEM (WSEM) was used in-situ to image the morphology of the aggregate in aqueous solution. Synthetic suspended particles were coagulated by two PACl products, a commercial product (PACl) and one laboratory product (PACl-E). The PACl-E contained more than 60% Al(13) while the PACl contained only 7% Al(13), with large percentage of colloidal Al. For coagulation by PACl at neutral pH and high dosage where the strong repulsion between particles occurs, the enmeshment ruled by reaction-limited aggregation (RLA) results in larger sweep flocs as well as higher fractal dimensional structure. For coagulation by PACl-E at alkaline pH and low dosage, the flocs were coagulated predominately by electrostatic patch with Al(13) aggregates. At such condition, it is likely that diffusion-limited aggregation (DLA) predominately rule PACl-E coagulation. The fractal dimension (D(s)) values of PACl and PACl-E flocs formed at enmeshment and electrostatic patch increased with dosage, respectively. When breakage of flocs occurs, the breakage rate of PACl-E flocs is slower than that of sweep flocs. By WSEM imaging, the adsorption of spherical Al precipitates onto the particles was observed to form sweep flocs with a rough and ragged contour, while the PACl-E flocs were formed with a smooth and glossy structure.

Biotreatment of H2S- and NH3-containing waste gases by co-immobilized cells biofilter

Gas mixture of H2S and NH3 in this study has been the focus in the research area concerning gases generated from the animal husbandry and the anaerobic wastewater lagoons used for their treatment. A specific microflora (mixture of Thiobacillus thioparus CH11 for H2S and Nitrosomonas europaea for NH3) was immobilized with Ca-alginate and packed inside a glass column to decompose H2S and NH3. The biofilter packed with co-immobilized cells was continuously supplied with H2S and NH3 gas mixtures of various ratios, and the removal efficiency, removal kinetics, and pressure drop in the biofilter was monitored. The results showed that the efficiency remained above 95% regardless of the ratios of H2S and NH3 used. The NH3 concentration has little effect on H2S removal efficiency, however, both high NH3 and H2S concentrations significantly suppress the NH3 removal. Through product analysis, we found that controlling the inlet ratio of the H2S/NH3 could prevent the biofilter from acidification, and, therefore, enhance the operational stability. Conclusions from bioaerosol analysis and pressure drop in the biofilter suggest that the immobilized cell technique creates less environmental impact and improves pure culture operational stability. The criteria for the biofilter operation to meet the current H2S and NH3 emission standards were also established. To reach Taiwans current ambient air standards of H2S and NH3 (0.1 and 1 ppm, respectively), the maximum inlet concentrations should not exceed 58 ppm for H2S and 164 ppm for NH3, and the residence time be kept at 72 s.