Now showing 1 - 10 of 75
  • Publication
    A review on numerous modeling approaches for effective, economical and ecological treatment wetlands
    (Elsevier, 2011-03) ;
    Constructed wetlands (CWs) for wastewater treatment have evolved substantially over the last decades and have been recognized as an effective means of “green technology” for wastewater treatment. This paper reviews the numerous modeling approaches ranging from simple first-order models to more complex dynamic models of treatment behaviour in CWs. The main objective of the modeling work is to better understand the process in CWs and optimize design criteria. A brief study in this review discusses the efforts taken to describe the process based model for the efficient removal of pollutants in CWs. Obtaining better insights is essential to understand the hydraulic and biochemical processes in CWs. Currently, employed modeling approaches can be seen in two categories, i.e. “black-box models” and “process-based models”. It is evident that future development in wetland technology will depend on improved scientific knowledge of internal treatment mechanisms.
    Scopus© Citations 86  5951
  • Publication
    Effectiveness of a drinking-water treatment sludge in removing different phosphorus species from aqueous solution
    Drinking-water treatment sludge (DWTS) produced at water treatment plants is an inescapable by-product and has long been treated as a waste for landfill. In this study, a series of batch adsorption tests were conducted using a wide range of phosphorus (P) species to determine the adsorption capacities of freshly dewatered aluminium salt based DWTS. The adsorption process is highly dependant on the pH of the suspension and is good at low pHs with adsorption capacities in the order of orthophosphate>polyphosphate>organic phosphate when these three P species were simulated according to their level in typical municipal wastewater. At pH 4.0, the adsorption capacity for orthophosphate was 10.2 mg-PO43-/g DWTS, polyphosphate was 7.4 mg-PO43-/g DWTS and organic phosphate was 4.8 mg-PO43-/g DWTS. Subsequently, a continuous flow column test with dewatered Al-based DWTS as filter medium was conducted at a hydraulic loading of 2.79 m3/m2.d and an extremely high P loading of 210.5 PO43-/m2.d. The sludge bed remained stable and removed over 80% P in a 30 day period and the bed did not reach saturation point for over 60 days. This proves the potential of the sludge as a filter material in various forms of P immobilization, thus converting it from a waste to a useful material in pollutant control.
    Scopus© Citations 188  4556
  • Publication
    High rate nitrogen removal in an alum sludge-based intermittent aeration constructed wetland
    A new development on treatment wetland technology for the purpose of achieving high rate nitrogen removal from high strength wastewater has been made in this study. The laboratory scale alum sludge-based intermittent aeration constructed wetland (AlS-IACW) was integrated with predenitrification, intermittent aeration, and step-feeding strategies. Results obtained from 280 days of operation have demonstrated extraordinary nitrogen removal performance with mean total nitrogen (TN) removal efficiency of 90% under high N loading rate (NLR) of 46.7 g N m–2 d–1. This performance was a substantial improvement compared to the reported TN removal performance in literature. Most significantly, partial nitrification and simultaneous nitrification denitrification (SND) via nitrite was found to be the main nitrogen conversion pathways in the AlS-IACW system under high dissolved oxygen concentrations (3–6 mg L–1) without specific control. SND under high dissolved oxygen (DO) brings high nitrogen conversion rates. Partial nitrification and SND via nitrite can significantly reduce the demand for organic carbon compared with full nitrification and denitrification via nitrate (up to 40%). Overall, these mechanisms allow the system to maintaining efficient and high rate TN removal even under carbon limiting conditions.
      1171Scopus© Citations 178
  • 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.
    Scopus© Citations 153  1907
  • Publication
    Two strategies for improving animal farm wastewater treatment in reed beds
    (Taylor & Francis, 2010-09) ;
    In this study, dewatered alum sludge cakes were used as substrate in a laboratory scale tidal vertical flow reed bed system treating animal farm wastewater. The “tidal flow” operation was employed to enhance oxygen transfer into the reed bed system, while dewatered alum sludge cake was used to enhance phosphorus (P) removal in the system through ligand exchange. Except for the removal of P which was consistently high throughout the experiment, the removal of organics (BOD5, COD) exhibited a trend of gradual and increasing removal. This highlights the obvious advantage of the use of the dewatered alum sludge cake in the reed bed. For the removal of organics, a mean removal percentage of 82.3 ± 3.5 % was obtained for BOD5 at an average loading of 84.6 g/m2.d. In addition, the first-order kinetics constant for BOD5 removal (KBOD, m/d) obtained in the system was about 9 times the rate constant commonly obtained in conventional horizontal flow systems. The mean level of dissolved aluminium (Al) monitored in the effluent was 0.04 ± 0.01 mg/l and this is well below the discharge limit of 0.2 mg/l for Al discharge into all waters.
    Scopus© Citations 6  1939
  • 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.
      422Scopus© Citations 9
  • Publication
    Phosphorus recovery as AlPO 4 from beneficially reused aluminium sludge arising from water treatment
    (Informa UK (Taylor & Francis), 2013-01) ; ;
    The purpose of this study was to develop an efficient and, possibly, a practically operated methodology to recover phosphorus (P) from P-saturated dewatered aluminium sludge cakes (DASC) after the DASC have been beneficially reused as constructed wetlands substrate for P-rich wastewater treatment. A three-step procedure of 1) P extraction by H 2SO 4, 2) decolorization of extraction leachate via H 2O 2 oxidation, and 3) AlPO 4 precipitation by pH adjustment, has been explored. The optimal conditions to form the precipitates of AlPO 4 were determined, with 97% of P and 99% of Al being recovered. The obtained compounds were identified by XRD, FTIR and SEM analyses. Although the purity, structure, characteristics and production control of the compounds are worthy of further investigation, this study provides a showcase of a ‘closed loop’ regarding the beneficial reuse of a ‘waste’ and the recovery of useful elements after the reuse.
    Scopus© Citations 16  546
  • Publication
    Current status of pesticides application and their residue in the water environment in Ireland
    (Informa UK (Taylor & Francis), 2013-02) ; ; ;
    Pesticides have been listed by the Irish Environmental Protection Agency as potentially dangerous pollutants that may pose a significant risk to the water environment in the Republic of Ireland (ROI). Although this analysis of pesticides data was based on the existing pesticides application survey in ROI, this study aims to produce a geographical information system profile for the amount of pesticides used in agriculture and the distribution of their use in different parts of the country. The study identifies and reports on the six most widely used pesticides in ROI, they are MCPA, Glyphosate, Chlorothalonil, Mecoprop-P, Chlormequat and Mancozeb. More significantly, the study discusses the application of pesticides and their potential impact on the Irish water environment by examining the status of pesticide residue in the Irish water environment. Finally, the study surveys possible strategies for the removal of pesticides residues, with attention to some of the studies done worldwide.
    Scopus© Citations 8  5730
  • 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.
    Scopus© Citations 12  657
  • Publication
    Constructed wetlands for environmental pollution control : a review of developments, research and practice in Ireland
    For the purpose of synthesizing a compendium of efforts aimed at environmental pollution control through the use of constructed wetlands systems (CWs) in Ireland, a detailed review of CWs was undertaken. Emphasis was placed on the diverse range of development, practice and researches on CWs technology, placing them in the overall context of the need for low-cost and sustainable wastewater treatment systems. The potential use of CWs in protecting estuarine quality within the current legislative framework is considered, as well as the emerging concept of integrated constructed wetlands (ICWs). In addition, an assessment of the efficiency of CWs in operation in Ireland towards abating environmental pollution was done, and compared with CWs operating in other European countries. The need for sufficient and appropriate data to assist in further development of CWs and modelling studies, and instilling confidence in the public is also highlighted.
    Scopus© Citations 164  11145