Now showing 1 - 7 of 7
  • Publication
    Optimising the performance of a lab-scale tidal flow reed bed system treating agricultural wastewater
    A gravel-based tidal flow reed bed system was operated with three different strategies in order to investigate its optimal performance for the treatment of high strength agricultural wastewaters. According to the three strategies, individual reed beds of the system were saturated and unsaturated with the wastewaters for different periods while steady hydraulic and organic loadings were maintained. Experiment results demonstrated that the system produced highest pollutant removal efficiencies with relatively short saturated period and long unsaturated period, highlighting the importance of O2 transfer into reed bed matrices during the treatment of high strength wastewaters. Significant removals of some major organic and inorganic pollutants were achieved with all the three operation strategies. Nitrification was not the major route of NH4-N removal when the system was under high organic loading. Due to the filtration of suspended solids and accumulation of biomass, gradual clogging of the reed bed matrices took place. The clogging caused concerns over the long-term efficiency of the current tidal flow reed bed system.
  • Publication
    On the role of gypsum (CaSO_4.2H_2O) in conditioning and dewatering of a waterworks sludge
    (Guangzhou University, 2004) ; ;
    Problems concerning the management and utilization of sludge derived from water treatment processes are still not fully solved. A common approach is direct discharge to a landfill site. This study provides experimental data to demonstrate the effectiveness of a combination of gypsum (CaSO4x2H2O) and an organic polymer in alum sludge conditioning and dewatering. Experimental results demonstrated that the filterability of dually conditioned alum sludge was significantly improved by the addition of gypsum at a 1:1 ratio (WT/WT) to original sludge solids. Dewatering tests showed that a further decrease of almost seven percentage of sludge cake equilibrium moisture content was achieved by the involvement of gypsum compared to the situation of single polymer conditioning. The importance of this study lies in the possible application of dewatered alum sludge to land use or as a filter medium in constructed wetland for wastewater treatment, providing a positive solution to the problem of alum sludge disposal.
  • Publication
    Removal of ammoniacal-nitrogen from an artificial landfill leachate in downflow reed beds
    The fate of ammoniacal-nitrogen (NH4-N) was studied in a lab-scale downflow reed bed system treating an artificial landfill leachate. Individual reed beds were submerged by the leachate, then drained and rinsed by tap water. It was discovered that NH4-N was removed by a two-staged process, adsorption onto the reed bed media followed by nitrification into nitrite-nitrogen (NO2-N) and nitrate-nitrogen (NO3-N). A drop of NH4-N level of the leachate was observed when the reed beds were submerged. By rinsing of the beds, part of the NH4-N adsorbed inside the bed matrices was re-released into the rinse water. The presence of NO2-N and NO3-N in the rinse water demonstrated that nitrification process took place while the NH4-N was being retained inside the bed matrices. For artificial leachates with NH4-N levels of 150±5 mg/l, an average removal rate of 43.8% in a three-hour treatment was achieved; mass balance analysis indicated that processes of adsorption, and transformation into NO2-N and NO3-N accounted for 63.7%, 4.3% and 24.4% of the NH4-N removal, respectively. This study also demonstrated that in general greater recirculation rate of effluent around the downflow reed beds gives higher NH4-N removal.
      1599Scopus© Citations 41
  • Publication
    An alternative arrangement of gravel media in tidal flow reed beds treating pig farm wastewater
    The effect of using coarse grain in the upper layer of a gravel-based reed bed is investigated. The aim for testing the “anti-sized” arrangement of gravel media is to seek a solution for the practical problem of medium clogging in reed beds that frequently takes place during the treatment of high strength wastewaters. Results from parallel operations of an anti-sized and a conventional “mono-sized” reed bed reveal that the former has the advantage of greater pollutant removal efficiencies. A specific clogging tendency rate is defined to quantitatively describe the clogging behaviour. Calculation of the clogging tendency rate reveals that the anti-sized reed bed has a clear advantage over the mono-sized bed because of improved ability to counteract clogging. Greater pore space in the upper layer of the anti-sized bed allows the suspended solids to be filtered and penetrate farther into the bed matrix, thereby allowing the solid-storage capacity of the matrix to be used more effectively and prolonging the operational life time of the bed. As such, the anti-sized arrangement of reed bed media may provide a viable solution for the problem of clogging.
      1216Scopus© Citations 26
  • Publication
    Anti-sized reed bed system for animal wastewater treatment : a comparative study
    Two separate sets of reed bed systems were operated in parallel for the purpose to study a comparative behaviour of high strength animal wastewater treatment. Each system consisted of five-stage gravel-based reed beds. The only difference between the two systems lies in the gravel arrangement within the beds. One system employed single sized gravel as bed medium (termed as mono-sized bed) while the other used two layers of gravel with coarse grain as the upper layer (termed as anti-sized bed). It was demonstrated that both the systems have the strong capacity for animal wastewater treatment but no significant difference with regard to pollutants‟ removal efficiency. However, anti-sized system showed a clear advantage in its ability to retard the clogging phenomenon exhibited during the system operation and avoid the impairment of its long-term functioning and sustainability. Clogging development was monitored via daily record of evolution of water level after the reed bed fill-up step in tidal flow operation strategy. According to present study, anti-sized reed bed experienced more than 2-fold operating period without clogging as compared with mono-sized reed bed in their parallel operation. In addition, a conceptual model to predict the clogging time was attempted and its utility was demonstrated via the data of this study.
      1929Scopus© Citations 86
  • Publication
    Enhanced removal of organic matter and ammoniacal-nitrogen in a column experiment of tidal flow constructed wetland system
    This study investigated the efficiency of a four-stage tidal flow constructed wetland system for the removal of organic matter and ammoniacal-nitrogen from diluted piggery wastewater. The results demonstrated that the operation of tidal flow enhanced the transfer of oxygen into wetland matrices. The overall oxygen consumption rate in the tidal flow system (357 gO2/m2∙d) was considerably higher than the rate obtainable in conventional wetlands. Most oxygen consumption (99%) was due to the decomposition of organic matter. The total supply of oxygen into the wetlands (473 gO2/m2∙d) exceeded the demand for the treatment. The percentage removal of BOD5 and NH4-N was improved by effluent recirculation at a ratio of 1:1. Immobilization by microbial cells and adsorption were found to be the main routes for the removal of ammoniacal-nitrogen. Significant nitrification could not take place under the treatment condition of the experiment.
      4435Scopus© Citations 178
  • Publication
    Purification capacity of a highly loaded laboratory scale tidal flow reed bed system with effluent recirculation
    The purification capacity of a laboratory scale tidal flow reed bed system with final effluent recirculation at a ratio of 1:1 was investigated in this study. In particular, the four-stage reed bed system was heavily loaded with strong agricultural wastewater. Under the hydraulic and organic loading rates of 0.43 m3/m2.d and 1055 gCOD/m2.d, respectively, the average removal efficiencies obtained for COD, BOD5, SS, NH4-N and P were 77%, 78%, 66%, 62% and 38%, respectively. Even with the high loading rates, about 30% of NH4-N was converted into NO2-N and NO3-N from the mid-stage of the system where nitrification took place. The results suggest that the multi-stage reed bed system could be employed to treat strong wastewater under high loading, especially for the substantive mass removal of solids, organic matter and ammoniacal-nitrogen. Tidal flow combined with effluent recirculation is a favourable operation strategy to achieve this objective.
      934Scopus© Citations 80