Now showing 1 - 10 of 29
  • Publication
    From "fills" to filter : insights into the reuse of dewatered alum sludge as a filter media in a constructed wetland
    (DesTech Publications, 2007-07) ; ; ;
    Dewatered alum sludge, a by-product of drinking water treatment plants, hitherto consigned to landfills was used to develop a novel bio-filter in form of a constructed wetland. Performance results have demonstrated the benefits of the alum sludge cakes in a lab-scale system in enhancing phosphorus (P) removal from an animal farm wastewater. Although P and organic matter were concurrently removed in the system, there was a probable “one off” release of organics from the system, and this coincided with an increase in inlet P concentration from 39.2 mg-P/l to 163.0 mg-P/l. A conceptual model was then proposed to explain and discuss this.
  • Publication
    An innovative solution for managing waterworks sludge : developing an alum sludge-based multi-stage constructed wetland system for wastewater treatment
    Waterworks sludge continues to be an inescapable by-product of the potable water treatment process. Accordingly, final disposal of the sludge remains one of the most significant pressing problems for the potable water treatment industry. The possibility of reusing the sludge as a main substrate in a novel constructed wetland system was investigated in this study. Results show that significant phosphorus (P) and other pollutants removal were achieved in the system. With a mean influent BOD5 (5-day biochemical oxygen demand) and COD (chemical oxygen demand) levels of 392.7 mg/l and 579.8 mg/l, respectively, a removal efficiency of 90.6 % and 71.8 %, respectively, was obtained. P removal was however exceptionally high despite the high influent mean P level of 45.3 mg-P/l, which is about 2-3 times the level of P commonly found in sewage. This is attributable to the P adsorption capacity of the alum sludge and this highlights the benefits of its reuse in the system. The paper presents and discusses the findings from a laboratory scale research, which has potential for further large scale implementation.
  • Publication
    Pilot field-scale demonstration of a novel alum sludge-based constructed wetland system for enhanced wastewater treatment
    In this study, beneficial reuse of the alum-contained drinking water treatment sludge is extended into developing a novel constructed wetland system (CWs) using the alum sludge as main substrate. The study reports on the first pilot field-scale alum sludge-based CWs operated in the tidal flow mode with enhanced capacity for phosphorus and organic matter removal from animal farm wastewater. The concept of the development is presented and this is followed by the performance analysis of the first CWs of its kind. The CWs consists of four identical compartments in series operated using a tidal flow strategy with a hydraulic loading rate of 0.29 m3/m2.d. First year analysis of the system’s performance shows that it is a unique and promising low-cost wastewater treatment system. The mean monthly removal efficiencies obtained was determined to range from 57%-84%, 36%-84%, 11%-78%, 49%-93%, 75%-94%, 73%-97% and 46%-83% for BOD5, COD, TN, NH4-N, TP, P (inorganic phosphorus) and SS. The system showed a distinct phosphorus removal and also, the system was effective in reducing levels of organics and ammonium-nitrogen. More importantly, the system showcases a novel reuse alternative for the alum sludge as opposed to its landfilling, demonstrating a win-win technique with a great potential for larger-scale application.
      1925Scopus© Citations 154
  • Publication
    Effects of livestock wastewater variety and disinfectants on the performance of constructed wetlands in organic matters and nitrogen removal
    Background, aim and scope: Treatment performance of constructed wetlands (CWs) is largely dependent on the characteristics of the wastewater. Although livestock wastewater is readily biodegradable in general, its variety in biodegradability can still be significant in practice. In addition, it is a common practice to periodically use disinfectants in livestock activities for health concerns. Obviously, the residual of the disinfectants in livestock wastewater may have serious inhibitory effect on the microbial activities during wastewater treatment. Thus, the main objective of this study was to examine the variety of livestock wastewater in biodegradability and its effect on the performance of a pilot scale tidal flow CWs (TFCWs) in organic matter and nitrogen removal. Furthermore, investigation of the potential inhibition of the chosen disinfectants on organic matter biodegradation and nitrification was another aim of this study. Materials and methods: The TFCWs system consisted of four-stage downflow reed beds with a hydraulic loading rate of 0.29 m3/m2·per day. Long-term stored livestock wastewater and fresh livestock wastewater were used, respectively, as feed to the system in different periods. Meanwhile, batch aeration tests were carried out to investigate the difference in biodegradation of the two types of wastewaters. Inhibitions of two types of disinfectants, namely UNIPRED and HYPROCLOR ED, on microbial activities were investigated in laboratory batch tests, with dosage of from 0.05% to 0.5%. Results: With fresh livestock wastewater, removal efficiencies of up to 93% and 94% could be achieved with average of 73% and 64% for chemical oxygen demand (COD) and TN, respectively. The performance deteriorated when the system was fed with long-term stored wastewater. In the batch tests, the long-time stored wastewater was characterized as non-biodegradable or at least very slowly biodegradable, while the fresh wastewater was readily biodegradable. UNIPRED showed very strong inhibition on both heterotrophic organisms and nitrifiers. Tested inhibition started from content of 0.05%, which is 1/10 of the recommended usage rate. Inhibitory effect of HYPROCLOR ED on COD degradation started from 0.1% and complete inhibition occurred from content of 0.3%, while significant inhibition on nitrification started from 0.1%. Conclusions: Livestock wastewater could vary significantly in biodegradability and it may turn to be non-biodegradable after a long-term storage. The variety of the livestock wastewater has a decisive influence on the performance of the CWs system, especially in TN elimination. In addition, the application of disinfectants UNIPRED and HYPROCLOR ED may cause serious inhibition on microbial activities and subsequent system failure.
      668Scopus© Citations 13
  • Publication
    Use of dewatered alum sludge as main substrate in treatment reed bed receiving agricultural wastewater : long-term trial
    This study aims to explore a novel application of dewatered alum sludge cakes (DASC) as the main medium in a single model reed bed to treat phosphorus-rich animal farm wastewater under "tidal flow" operation on a long term basis. It is expected that the cakes act as the carrier for developing biofilm and also serve as adsorbent to enhance phosphorus (P) immobilization. Results have demonstrated that average removal efficiencies of 73.3±15.9% for COD, 82.9±12.3% for BOD5, 86.4±6.0% for RP (reactive P), 88.6±7.2% for SRP (soluble reactive P) and 77.6±17.5% for SS can be achieved during the two year's operation. More significantly, the "P-adsorption proportion" by DASC in the reed bed is 42% of the overall P removal. The remaining removal of P may be contributed by the trapping and filtration process of DASC. Therefore, the lifetime of the DASC in reed bed is reasonably longer than that determined from the batch isotherm test.
      2217Scopus© Citations 97
  • Publication
    Process-based modelling of phosphorus removal in a novel constructed wetland system using dewatered alum-sludge as substrate
    A process-based model that can evaluate the transport and the fate of phosphorus (P) in agricultural wastewater was developed for a novel 4-stage dewatered alum sludge cakes (DASC) based constructed wetlands (CWs) system using STELLA software (version 9.1.4). The model considered adsorption, plant and microbial uptakes as the major forms of P involved in the transformation chains. The results were obtained by experimental procedure through laboratory measurement, from literature and/or calibration. The observed effluent P concentration in the CWs ranged from 3.62 to 8.50 mg/L (stage 1), 2.00 to 4.45 mg/L (stage 2), 1.39 to 3.76 mg/L (stage 3) and 0.52 to 2.36 mg/L (stage 4), whereas the simulated values ranged from 2.12 to 10.99 mg/L (stage 1), 1.32 to 5.65 mg/L (stage 2), 0.84 to 3.64 mg/L (stage 3) and 0.53 to 2.25 mg/L (stage 4), respectively. The simulated and observed values of P removal in the CWs system were in good agreement. A mass balance analysis was performed for all the major processes which resulted in a major pathway of P removal through adsorption (64–75%, 58–66%, 57–63% and 49–58%) followed by plant uptake (7–11%, 8–14%, 14–17% and 9–19%) and microbial uptake (3–7%, 3–5%, 9–12% and 7–12%) for stage 1, stage 2, stage 3 and stage 4, respectively. Thus the mathematical model developed in this study could be used to explain the removal processes and simulate the fate of P in the DASC-based CWs system.
      433Scopus© Citations 9
  • Publication
    Characteristics and mechanisms of phosphate adsorption on dewatered alum sludge
    The adsorption characteristics of phosphate adsorption on the dewatered alum sludge were identified as a function of pH and ion strengths in solution. In addition, adsorption mechanisms were investigated by conducting batch tests on both the hydrolysis and P-adsorption process of the alum sludge, and making a comparative analysis to gain newer insights into understanding the adsorption process. Results show that the adsorption capacity decreased from 3.5 to 0.7 mg-P/g-sludge when the solution pH was increased from 4.3 to 9.0, indicating that adsorption capacity is largely dependent upon the pH of the system. The results of the competitive adsorption between phosphate and typical anions found in wastewater, such as SO42- and Cl-, onto alum sludge reveal that alum sludge can selectively adsorb phosphate ions. The insignificant effect of SO42- and Cl- on P-adsorption capacity indicates that phosphate adsorption is through a kind of inner-sphere complex reaction. During the adsorption process, the decrease of phosphate concentration in solution accompanied with an increase in pH values and concentrations of SO42-, Cl- and TOC (total organic carbon) suggests that phosphate replaced the functional groups from the surface of alum sludge which infers that ligand exchange is the dominating mechanism for phosphate removal. At the same time, the simultaneous decreases in PO43- and total aluminium concentration in solution indicate that chemical reaction and precipitation are other mechanisms of phosphate removal.
      6252Scopus© Citations 364
  • Publication
    Multivariate-parameter optimization of acid blue-7 wastewater treatment by Ti/TiO2 photoelectrocatalysis via Box-Behnken design
    The aim of this study is to obtain optimal decolourization conditions for Acid blue-7 (AB7) wastewater treatment by Ti/TiO2 photoelectrocatalysis using response surface methodology (RSM). On the basis of a three-variable Box-Behnken design (BBD), RSM was used to determine the effect of pH values (ranged from 3.2 to 6), light intensity (ranged from 10 to 20 ×102μW/cm2) and bias potential (ranged from 0.1 to 1.1V) on the levels of response, i.e. decolourization efficiency. By applying the quadratic regression analysis, the equations describing the behaviors of the response as simultaneous functions of the selected independent variables were developed. Accordingly, the optimal conditions were determined as pH of 3.41, light intensity of 16.02×102μW/cm2 and bias potential of 0.68V. Decolourization efficiency of 90.13%, obtained experimentally under such optimal conditions was highly agreed with that of 90.44%, estimated by the equations.
      2015Scopus© Citations 47
  • Publication
    Constructed wetlands using aluminium-based drinking water treatment sludge as P-removing substrate : should aluminium release be a concern?
    (RSC Publishing, 2011-06) ; ;
    This study investigated an important issue of aluminium (Al) release in a novel reuse of Al-based water treatment sludge (Al-WTS) in constructed wetland system (CWs) as alternative substrate for wastewater treatment. Al-WTS is an inevitable by-product of drinking water treatment plants that use Al-salt as coagulant for raw water purification. It has recently been demonstrated that Al-WTS can be reused as a low-cost phosphorus (P) adsorbent and biofilm carrier in CWs for wastewater treatment. However, to facilitate the large scale application of Al-WTS in CWs as wetland substrate, concerns about Al leaching during its’ reuse in CWs must be addressed as Al is a dominant constituent in Al-WTS. In this study, a desk review of literature on Al release during Al-WTS reuse was conducted. Furthermore, a 42-week Al monitoring was carried out on a pilot field-scale CWs employing Al-WTS as main substrate. Results show that 22 out of the 35 studies reviewed, reported Al release with levels of soluble Al reported ranging from 0.01 to about 20 mg L-1. Monitoring of Al in the pilot field-scale CWs shows that there was Al leaching. However, except for the first three weeks of operation, effluents concentrations of both total- and soluble-Al were all below the general regulatory guideline limit of 0.2 mg L-1. Overall, the study addresses a very vital concern regarding the successful application of Al-WTS in CWs and shows that Al release during such novel reuse is quite low and should not preclude its use.
      1055Scopus© Citations 40
  • Publication
    Characterization of aluminium-based water treatment residual for potential phosphorus removal in engineered wetlands
    Aluminium-based water treatment residual (Al-WTR) is the most widely generated residual from water treatment facilities worldwide. It is regarded as a by-product of no reuse potential and landfilled. This study assessed Al-WTR as a potential phosphate-removing substrate in engineered wetlands for wastewater treatment. Results indicate the specific surface area ranged from 28.0 m2 g-1 to 41.4 m2 g-1 and this increased with increasing particle size. X-ray Diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and energy-dispersive X-ray spectroscopy all indicate that the Al-WTR is mainly composed of amorphous aluminium which influences its phosphorus (P) adsorption capacity. The pH and electrical conductivity ranged from 5.9 - 6.0 and 0.104 dS m-1 - 0.140 dS m-1 respectively, and both showed that it should suitably support plant growth. Batch tests showed a maximum P adsorption capacity of 31.9 mg-P g-1 and significant P removal was achieved in column tests. Overall, results showed that Al-WTR can be a low-cost, easily and locally available substrate for enhanced P removal in engineered wetlands and it carries the benefits of reuse of a by-product that promotes sustainability.
      10551Scopus© Citations 201