Tai Il Yoon

Wastewater treatment in a hybrid biological reactor using powdered minerals: effects of organic loading rates on COD removal and nitrification

A new hybrid biological reactor (HBR) using powders as a bio-carrier was developed, and compared to conventional activated sludge (AS) with increasing substrate organic loading rate (OLR) from 1.0 to 4.0 kg COD/m3 per day. The HBRs employed different powders of bentonite and clinoptilolite, respectively, and its concentration in an aeration basin was sustained at 500 and 4000 mg/l, separately. Biomass concentrations in the HBRs were greatly increased by biofilm formation attached on the powders, which were linearly augmented with OLR. The HBRs operated under 4000 mg/l of minerals concentration highly improved removal efficiencies of organic compounds as well as organic removal rates, although no significant advancement was found in the HBRs run under 500 mg/l, compared to conventional AS. This was probably attributed to high biomass concentration (the maximum value of 7100 mg MLVSS/l) by biofilms formed on the minerals. The efficiencies of total Kjeldahl nitrogen (TKN) removal and nitrification were decreased with increasing substrate COD to TKN (C/N) ratio. However, the HBR with 4000 mg/l of clinoptilolite concentration showed higher nitrification efficiency rather than that in other reactors, little depending on substrate C/N ratio varied. It could be concluded that high ammonium exchange capacity of the clinoptilolite enabled nitrfiers to colonize favourably in the biofilms on this mineral, which increased nitrification.

Resource recovery of sludge as a micro-media in an activated sludge process

Abstract An experiment was conducted to evaluate the feasibility of sludge reuse as a micro-medium in an activated sludge (AS) process. Two experimental protocols were employed. A conventional activated sludge was tested as a control, while the other involved addition of clinoptilolite (ZR) of which 4000 mg/l was unvaryingly sustained in an aeration basin. Two experiments were performed for ZR. In one, clinoptilolite was used as micro-media for 60 days (Model 1). The other used dried excess sludge for 55 days (Model 2). For sludge being recovered as micro-media, organic matter in the sludge was eliminated by 86% at 300 °C. It was completely removed at 500 °C within 30 min, which was regarded as the optimal drying condition. For Model 1, the concentration of biomass was increased by 4720 mg MLVSS/l. It was greater by a factor of two than that of the control. Moreover, it is shown that organic matter could be removed up to 95%. In addition, the sludge settling properties were greatly enhanced by clinoptilolite being implemented as floc seeds. Nitrification was considerably improved by more than 90%, due to the high concentration of nitrifiers attached to micro media. For Model 2, the improved performance was sustained on applying burned sludge into the AS. It was concluded that dried sludge could be reused as micro-media in an activated sludge process.

Hybrid Treatment of Tetramethyl Ammonium Hydroxide Occurring from Electronic Materials Industry

TMAH (tetramethyl ammonium hydroxide) originating from etching and photo-developing processes was treated with Fenton oxidation followed by an activated sludge. Additionally, a Microtox test was performed to address any potential toxicity of TMAH against mixed cultures of microorganisms in the activated sludge. The Microtox test revealed that toxicity of TMAH againstPhotobacterium phosphoreum was highly effective showing 5% of EC50, but its toxicity was completely dissipated showing 100% of EC50 being recovered after being treated with Fenton reagents. BOD5 test showed that acclimated cultures to TMAH could readily decompose TMAH in an order of magnitude higher than that of not-acclimated culture. Feasibility tests showed that TMAH was readily biodegraded after being oxidized by the Fenton process, while TMAH fed directly into the activated sludge was laggardly decomposed during longer adaptation period. In the presence of acetic acid, activity of acclimated mixed cultures to TMAH was considerably reduced by dominant presence of predators competitively utilizing acetic acid.

Comment on "the interaction of humic substances with cationic polyelectrolytes".

Kam and Gregory (Water Research 35(2001) 3557– 3566) reported on the removal of humic substances (HS) in the coagulation and flocculation process using cationic polyelectrolytes. The investigation was devoted to the dominant mechanism of HS removal in the process. The HS elimination was compared in a Jar test performed with cationic polymers of different charge and molecular weight under constant pH of 7. The experimental results showed that charge neutralization was a significant factor for the removal of aquatic HS in the coagulation/flocculation process, monitored by the colloid titration and the streaming current procedures, and indicated that a bridging mechanism was unlikely to play a major role in this process. The authors concluded that the key mechanism of charge neutrality was applied to the HS removal in the coagulation process of metal coagulants used, as well as cationic polymers. However, the former is questionable. In coagulation using metal coagulants, three kinds of mechanisms were commonly referred for the HS removal: (1) charge neutralization, (2) complexation, and (3) adsorption [1,2]. A dominant mechanism depends on the pH of a solution. Gregor et al. [2] noted that cationic Al ions formed complexes combined with acidic functional groups (carboxylic and phenolic groups) of HS in the pH condition below 5.5, and that the function (defined as complexation) prevalently attributed to the HS reduction under the pH region. The complexation was differentiated from charge neutralization in that the complex would be precipitated due to size increase rather than charge neutrality [2]. On the other hand, Bell-Ajy et al. [3] recently reported that at low pH conditions insoluble complexes could be established through charge neutralization between negative HS and cationic metal hydrolysis products. It is likely that at low pH values the key mechanism of the HS removal is not clarified yet in the coagulation process. It was reported that the adsorption of humic substances to alum flocs played a major role in the HS removal under pH 6–7 favoring Al hydroxide precipitation [4,5]. The adsorption of HS to Al hydroxide occurs through surface complexation or ligand exchange [6]. Here, the surface complexation means interactions between functional groups of HS and surface hydroxyl on Al hydroxide [7,8]. Bose and Reckhow [9] also suggested that the adsorption of HS to Al hydroxide floc was a prevalent process in removing aquatic HS. In this paper, it was concluded that charge neutralization was the key mechanism in the coagulation process using cationic polymers, and the phenomenon extended to the HS removal in the coagulation of metal salts employed without experimental validation. However, it has been demonstrated that the dominant mechanism for the HS removal seriously varies depending on the pH of the solution in the coagulation/flocculation process when metal salts are used as coagulants. It is likely that a supplementary experiment is required to evaluate the HS removal mechanism in the coagulation using metal coagulants.

Characterization and control of foulants occurring from RO disc-tube-type, membrane treating, fluorine manufacturing, process wastewater

Abstract This study was carried out to find a way to limit fouling of disc-tube-type reverse osmosis membranes in the treatment of acid rinse wastewater from the fluorine manufacturing process as well as to pretreat the wastewater before it entered the membrane process. Experiments showed that the scale consisted of Ca 2+ , SO 4 −2 and F − . Complex scales were removed in a subsequent procedure where the membrane was rinsed with NaOH followed by citric acid which could consequently recover its flux up to 86%. Cleaning chemicals had to be used regularly for efficient recovery of permeate flux. Ultrasonic cleaning could also improve the recovery of permeate flux up to 83%. Calcium salts were used to remove fluoride ions. CaCl 2 removed fluoride ions up to 11% more than Ca(OH) 2 at 0.5 [Ca 2+ ]/[F − ]. At acidic pH 4–7 or alkaline pH 7 and above, residual fluoride ions increased as Ca 2+ reacted more efficiently with Cl − , OH − and SO 4 −2 rather than F − . On the other hand, fluoride ions were best removed at pH 7. Adding Ca 2+ salt above pH 7 caused an increase of residual Ca 2+ salt in the effluent, even if fluoride ions can be ideally removed in the form of CaF 2 at a pH over 11.