Jun Nan

Effects of chloride ions on electro-coagulation-flotation process with aluminum electrodes for algae removal

Electro-coagulation-flotation (ECF) is one of the most promising technologies that offers an attractive alternative to conventional coagulation and flotation. In this study, the effectiveness and mechanisms of algae removal by ECF process using aluminum electrodes was investigated in the presence of Cl(-) ions. The results showed that the addition of Cl(-) ions (1.0, 3.0, 5.0 and 8.0 mM) had a promoting effect on the algae removal in terms of both the cell density and chlorophyll-a, which could be attributed to the following two reasons. Firstly, active chlorine could be generated in the ECF when Cl(-) ions were present. The electrochemically generated active chlorine was demonstrated to be effective for the inactivation of algae cells with the aid of the electric field in the ECF. Secondly, the Cl(-) ions in the algae solution could enhance the release of Al(3+) from the aluminum electrodes in the ECF. Through SEM-EDX analysis, pitting corrosion and alleviated formation of oxide film by Cl(-) ions were observed on the anode surface. When considering that Cl(-) ions are universally present in natural waters, the effects of Cl(-) on ECF process for algae removal are of great significance.

Consecutive chemical cleaning of fouled PVC membrane using NaOH and ethanol during ultrafiltration of river water

Chemical cleaning of fouled hollow-fiber polyvinyl chloride (PVC) membrane with the consecutive use of NaOH and ethanol during ultrafiltration of river water was investigated in the study. Results showed that through the chemical cleaning with 1% NaOH for 30min, a negative cleaning efficiency of -14.6% was observed for the PVC membrane. This might be due to the increase of membrane hydrophobicity, which was reflected by the increase of contact angle from 69.7 degrees to 87.6 degrees . On the other hand, the cleaning efficiency of 85.1% was obtained by the consecutive cleaning with 30min of 1% NaOH and 30min of ethanol. Individual ethanol cleaning could remove 48.5% of the irreversible resistance, indicating that NaOH cleaning also made its contribution (36.6%) to the removal of membrane foulants. Scanning electronic microscopy (SEM) and atomic force microscopy (AFM) analyses demonstrated that both NaOH and ethanol were not only able to eliminate the foulants on membrane surface, but also able to remove the in-pore fouling of the PVC membrane. The synergetic effects for removing membrane foulants were observed between the NaOH and ethanol. Furthermore, ethanol could also restore the hydrophilicity of the membrane by decreasing the contact angle from 87.6 degrees to 71.4 degrees . Considering that ethanol is easy to be used and reclaimed, the consecutive chemical cleaning by alkali and ethanol is recommended for PVC membrane in filtration of surface water.

Effect of PAC addition on immersed ultrafiltration for the treatment of algal-rich water

The aim of this study was to evaluate the effect of powdered activated carbon (PAC) addition on the treatment of algal-rich water by immersed ultrafiltration (UF), in terms of permeate quality and membrane fouling. Experiments were performed with a hollow-fiber polyvinyl chloride ultrafiltration membrane at a laboratory scale, 20-25°C and 10 L/(m(2) h) constant permeate flux. UF could achieve an absolute removal of Microcystis aeruginosa cells, but a poor removal of algogenic organic matter (AOM) released into water, contaminants responsible for severe membrane fouling. The addition of 4 g/L PAC to the immersed UF reactor significantly alleviated the development of trans-membrane pressure and enhanced the removal of dissovled organic carbon (by 10.9±1.7%), UV(254) (by 27.1±1.7%), and microcystins (expressed as MC-LR(eq), by 40.8±4.2%). However, PAC had little effect on the rejection of hydrophilic high molecular weight AOM such as carbohydrates and proteins. It was also identified that PAC reduced the concentrations of carbohydrates and proteins in the reactor due to decreased light intensity, as well as the MC-LR(eq) concentration by PAC adsorption.

Characteristic analysis on temporal evolution of floc size and structure in low-shear flow

A series of flocculation tests were performed to investigate the effect of low-shear rates (G = 3-16 s(-1)) on flocculation of kaolin suspension by polyaluminum chloride (PACl), with the goal of understanding floc growth mechanisms. Results were reported in terms of floc average size (d(p)) and boundary fractal dimension (D(pf)), derived from a non-intrusive optical sampling and digital image analysis technique. As expected, the rate of floc aggregation increased with increasing G, resulting in faster changes in aggregate size and structure in the initial stage of flocculation. Nevertheless, steady state was attained faster for D(pf) than for d(p) at the same shear rates, possibly due to the self-similarity of fractal aggregates. An interesting finding was that at G = 3 s(-1), an obvious plateau was observed for the average-size evolution at steady state; for shear rates of 6 and 7 s(-1), the flocs exhibited some decrease after reaching the peak of size, mainly as a result of floc settling at steady state; and for G = 11-16 s(-1), a decrease in floc size was possibly attributed to the irreversibility of PACl-floc breakage. The process of floc growth was described using a fractal growth model, which defined flocculation as the result of the combined processes of aggregation and restructuring. The conceptual model could effectively characterize temporal changes in floc size and structure, and found that fragmentation followed by reformation seemed to be more effective in forming larger and more compact aggregates than the restructuring process due to erosion and reformation, which may provide useful insights for the design of flocculation reactors.

Using bacterial catalyst in the cathode of microbial desalination cell to improve wastewater treatment and desalination.

A microbial desalination cell (MDC) is able to desalinate salt water without energy consumption whilst generating bioenergy. Previously MDCs used abiotic cathodes, which are restricted in application by high operating costs and low levels of sustainability whereas, in the present study, an aerobic biocathode consisting of carbon felt and bacterial catalysts was tested. The biocathode MDC produced a maximum voltage of 609 mV, the value of which was 136 mV higher than that of an air cathode MDC operated under the same conditions. The salinity of 39 mL of salt water (35 g L(-1) NaCl) was reduced by 92% using 0.441 L of anode solution (11.3:1), with a coulombic efficiency of 96.2 ± 3.8% and a total desalination rate of 2.83 mg h(-1). The biocathode MDC proved to be a promising approach for efficient desalination of salt water.

Chemical cleaning of fouled PVC membrane during ultrafiltration of algal-rich water.

Cleaning of hollow-fibre polyvinyl chloride (PVC) membrane with different chemical reagents after ultrafiltration of algal-rich water was investigated. Among the tested cleaning reagents (NaOH, HCl, EDTA, and NaClO), 100 mg/L NaClO exhibited the best performance (88.4% +/- 1.1%) in removing the irreversible fouling resistance. This might be attributed to the fact that NaClO could eliminate almost all the major foulants such as carbohydrate-like and protein-like materials on the membrane surface, as confirmed by Fourier transform infrared spectroscopy analysis. However, negligible irreversible resistance (1.5% +/- 1.0%) was obtained when the membrane was cleaning by 500 mg/L NaOH for 1.0 hr, although the NaOH solution could also desorb a portion of the major foulants from the fouled PVC membrane. Scanning electronic microscopy and atomic force microscopy analyses demonstrated that 500 mg/L NaOH could change the structure of the residual foulants on the membrane, making them more tightly attached to the membrane surface. This phenomenon might be responsible for the negligible membrane permeability restoration after NaOH cleaning. On the other hand, the microscopic analyses reflected that NaClO could effectively remove the foulants accumulated on the membrane surface.

Characteristic analysis on morphological evolution of suspended particles in water during dynamic flocculation process

The evolution of floc morphology during constant-speed and variable-speed flocculation was examined to understand floc growth mechanisms. Flocculation-test results were reported in terms of floc average size and fractal dimension, derived from in situ optical sampling and image analysis. The morphological evolution was also described using a fractal growth model, which defined flocculation as the combined processes of aggregation and restructuring. During constant-speed flocculation, aggregation rate increased with increasing shear, but breakage became significant. Also, a decrease was observed after reaching the peak of size, possibly due to floc settling in low shear and the irreversibility of breakage in high shear. The development of floc morphology in variable-speed flocculation indicated that the surface nature of initial flocs was critical to form larger final flocs, because aggregates with irregular shape had more connection spots than those with smooth surface, thus producing a higher aggregation...

Hybrid process of BAC and sMBR for treating polluted raw water

The hybrid process of biological activated carbon (BAC) and submerged membrane bioreactor (sMBR) was evaluated for the drinking water treatment from polluted raw water, with the respective hydraulic retention time of 0.5 h. The results confirmed the synergetic effects between the BAC and the subsequent sMBR. A moderate amount of ammonium (54.5%) was decreased in the BAC; while the total removal efficiency was increased to 89.8% after the further treatment by the sMBR. In the hybrid process, adsorption of granular activated carbon (in BAC), two stages of biodegradation (in BAC and sMBR), and separation by the membrane (in sMBR) jointly contributed to the removal of organic matter. As a result, the hybrid process managed to eliminate influent DOC, UV(254), COD(Mn), TOC, BDOC and AOC by 26.3%, 29.9%, 22.8%, 27.8%, 57.2% and 49.3%, respectively. Due to the pre-treatment effect of BAC, the membrane fouling in the downstream sMBR was substantially mitigated.

Photo-fermentative bacteria aggregation triggered by L-cysteine during hydrogen production

BackgroundHydrogen recovered from organic wastes and solar energy by photo-fermentative bacteria (PFB) has been suggested as a promising bioenergy strategy. However, the use of PFB for hydrogen production generally suffers from a serious biomass washout from photobioreactor, due to poor flocculation of PFB. In the continuous operation, PFB cells cannot be efficiently separated from supernatant and rush out with effluent from reactor continuously, which increased the effluent turbidity, meanwhile led to increases in pollutants. Moreover, to replenish the biomass washout, substrate was continuously utilized for cell growth rather than hydrogen production. Consequently, the poor flocculability not only deteriorated the effluent quality, but also decreased the potential yield of hydrogen from substrate. Therefore, enhancing the flocculability of PFB is urgent necessary to further develop photo-fermentative process.ResultsHere, we demonstrated that L-cysteine could improve hydrogen production of Rhodopseudomonas faecalis RLD-53, and more importantly, simultaneously trigger remarkable aggregation of PFB. Experiments showed that L-cysteine greatly promoted the production of extracellular polymeric substances, especially secretion of protein containing more disulfide bonds, and help for enhancement stability of floc of PFB. Through formation of disulfide bonds, L-cysteine not only promoted production of EPS, in particular the secretion of protein, but also stabilized the final confirmation of protein in EPS. In addition, the cell surface elements and functional groups, especially surface charged groups, have also been changed by L-cysteine. Consequently, absolute zeta potential reached a minimum value at 1.0 g/l of L-cysteine, which obviously decreased electrostatic repulsion interaction energy based on DLVO theory. Total interaction energy barrier decreased from 389.77 KT at 0.0 g/l of L-cysteine to 127.21 kT at 1.0 g/l.ConclusionsThus, the strain RLD-53 overcame the total energy barrier and flocculated effectively. After a short settlement, the biomass rush out will be significantly reduced and the effluent quality will be greatly improved in the continuous operation. Furthermore, aggregation of PFB could enable high biomass hold-up of photobioreactor, which allows the photobioreactor to operate at low hydraulic retention time and high organic loading rate. Therefore, the described flocculation behaviour during photo-hydrogen production is potentially suitable for practicable application.

Photo-hydrogen production by Rhodopseudomonas faecalis RLD-53 immobilized on the surface of modified activated carbon fibers

abstract In the present study, the effect of Ni 2þ (0–10 mmol/l), Fe (0–200 mmol/l) and Mg 2þ (0–15 mmol/l) concentration on photo-hydrogen production from acetate was investigated bybatch culture. Results showed that under a proper concentration range, Ni 2þ was able toenhance the hydrogen production rate and the hydrogen yield; Fe 2þ was able to increasethe hydrogen yield, and hydrogen production rate was enhanced only when the culturingtime was 24–72 h. Ni 2þ and Fe 2þ at a higher concentration inhibited cell growth. When Ni 2þ and Fe 2þ concentrations were 4 mmol/l and 80 mmol/l, respectively, maximal hydrogen yieldof 2.87 and 2.78 mol H 2 /mol acetate was obtained when batch culturing at 35 C with initialpH 7.0. Mg 2þ did not significantly affect hydrogen production and hydrogen yield whichmaintained at about 2.45 mol H 2 /mol acetate, but it was favorable to cell growth.a 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rightsreserved. 1. Introduction