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Abstract: Dewatered alum sludge, a widely generated by-product of drinking water treatment plants using aluminium salts as coagulants was used as main substrate in a pilot on-site constructed wetland system treating agricultural wastewater for 11months. Treatment performance was evaluated and spreadsheet analysis was used to establish correlations between water quality variables. Results showed that removal rates (in g/m2 d) of 4.6–249.2 for 5day biochemical oxygen demand (BOD5), 35.6–502.0 for chemical oxygen demand (COD), 2.5–14.3 for total phosphorus (TP) and 2.7–14.6 for phosphate (PO4 chieved. Multiple regression analysis showed that effluent BOD5 and COD can be predicted to a reasonable accuracy (R 2 =0.665 and 0.588, respectively) by using input variables which can be easily monitored in real time as sole predictor variables. This could provide a rapid and cheap alternative to such laborious and time consuming analyses and also serve as management tools for day-to-day process control. [Copyright &y& Elsevier]

Abstract: 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 0.29m3/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 were determined that ranged 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, respectively. 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. [Copyright &y& Elsevier]

Abstract: The concept, design and performance analysis of a four-stage novel constructed wetland system (CWs) capable of enhanced and simultaneous removal of phosphorus (P) and organic matter (OM) from wastewaters is described. Alum sludge, a largely available by-product of drinking water facilities using aluminium salts as coagulant was used as the media. Under a hydraulic loading rate of 1.27m3/m2 d and a range of organic loading rate of 279.4–774.7g-BOD5/m2 d and 361.1–1028.7g-COD/m2 d, average removal efficiencies (mean±SD) of 90.6±7.5% for BOD5 and 71.8±10.2% for COD were achieved, respectively. P removal was exceptional with average removal efficiency of 97.6±1.9% achieved for soluble reactive P at a mean influent concentration of 21.0±2.9mg/l. Overall, the system holds great promise as a novel CWs for simultaneous removal of P and OM, and at the same time, it transforms alum sludge from a waste into a useful material. [Copyright &y& Elsevier]

Abstract: In line with the increasing studies on the beneficial reuse of alum sludge from a “waste” into useful raw material, this paper reports an in-depth investigation of the effects of ageing time on the structure and the phosphate adsorption capacity of a dewatered alum sludge obtained from a local drinking water treatment plant in Ireland. During the ageing period from 0 day to up to 18 months, the adsorption capacity of the sludge varied from 21.4 to 23.9mgPg−1 sludge at pH 4.3, 14.3 to 14.9mgPg−1 sludge at pH 7.0 and 0.9 to 1.1mgPg−1 sludge at pH 9.0, respectively, indicating marginal effect of ageing time on such sludge''s ability to adsorb phosphate. This result seems in conflict with other studies reported in the literature. To reveal such, series of investigations including physicochemical characterization, morphological structure, Brunauer–Emmett–Teller (BET) surface area and porous structure of the aged sludge were carried out. All the results conclusively show that ageing time has an insignificant effect on the structure and properties of the dewatered alum sludge and therefore, the phosphate adsorption capacity of the alum sludge shows insignificant change during the ageing process. [Copyright &y& Elsevier]

Alternative conditioning of aluminium-based drinking water treatment sludge using Fenton reagent (Fe2+/H2O2) was examined in this study. Focuses were placed on effectiveness and factors to affect such novel application of Fenton process. Experiments have demonstrated that considerable improvement of alum sludge dewaterability evaluated by capillary suction time (CST) can be obtained at the relative low concentrations of Fenton reagent. A Box-Behnken experimental design based on the response surface methodology was applied to evaluate the optimum of the influencing variables, i.e. iron concentration, hydrogen peroxide concentration and pH. The optimal values for Fe2+, H2O2, and pH are 21mgg−1 DS−1(dry solids), 105mgg−1 DS−1 and 6, respectively, at which the CST reduction efficiency of 48±3% can be achieved, this agreed with that predicted by an established polynomial model in this study. [Copyright &y& Elsevier]

On the basis of experiments carried out using an image analysis system and static zone settlement, the alum sludge floc structure and the floc packing status with varied polymer dosages were examined in greater detail to reveal the link with the settling behaviour manifested in the “CML30 method”. The results of image analysis lead to the findings of the floc size with a pattern in initially great increase with low polymer dose and finally a plateau being reached at higher amount of polymer addition. Meanwhile, a polymer dosage in the range of 2.0–20.0 mg/l (for sludge SS=4,595 mg/l) can result in the increase of the floc fractal dimension (DF) up to an average value of 1.72 (raw sludge DF being 1.06), indicating greater compactness of the floc solids. These floc features control the settling behaviour of the “CML30 method”, especially in small polymer dosages. However, in large polymer doses, the controlling factor is derived from the floc ‘packing’ status (referring to the inter–floc contact manner). This ‘packing’ status may associate with viscosity of settling medium (supernatant) and the excess polymer in bulk solution. All these affect the sludge floc networked structure in overdosing range. [Copyright &y& Elsevier]

Discusses the use of polymers for conditioning alum sludge derived from the coagulation of low turbidity colored waters. Applications of polymers in water treatment; Concept of optimum dose for water and wastewater sludge; Specifications of solids feed.

This paper aims to examine the correlations between floc physical properties, such as size, density, structure (in terms of fractal dimension) and optimum dosage in an alum sludge conditioning with organic polymer and also dewatering using an air pressure plate apparatus. Initially, optimum dosage was evaluated by a modified specific resistance to filtration (SRF). Thereafter, floc size, density and structure were examined in greater detail by means of an image analysis system. The results of this investigation reveal that: (1) polymer conditioning of alum sludge can result in a significant increase of floc size with a plateau to be reached in higher dosages; (2) higher floc effective densities are associated with larger doses; and (3) increased fractal dimensions are associated with increased dose, particularly in small dosages, this reflecting the increased compactness of floc structure. However, no direct correlation was found between floc physical properties and optimum dose both in conditioning and dewatering except for the weak correlation in floc size and optimum dosage. [Copyright &y& Elsevier]

A previous study demonstrated that red gypsum could be used as skeleton builder in combination with a polymer for conditioning an alum sludge. Sludge filterability in terms of net sludge solids yield (YN) was improved under the mechanism of interaction between polymer and gypsum. In this study, the dewatering behaviour of an alum sludge conditioned dually with a polymer and red gypsum was investigated using a Lab-scale air pressure plate. Groups of experiments were designed to assess the influence of gypsum on the significance of the extent of dewatering. Experimental data showed that the involvement of the gypsum could enhance the dewatering extent by further decreasing equilibrium moisture content (MC) in 7 percentages comparing with the situation of the absence of gypsum. By examining the controlling factors, it is noted that the gypsum associated with polymer can form the more compact sludge floc (evaluated in terms of fractal dimension, DF). This may help to build up a more porous, permeable and rigid lattice structure, which retains solid particles and allows the water to be transmitted. The enhancement of dewatering extent is mainly contributed to the beneficial structure. Interaction of polymer and gypsum is a key factor in the improved dewatering behaviour since gypsum by itself can hardly benefit the dewatering process in the case examined in this study. [Copyright &y& Elsevier]

In this study, combinations of applied pressure, pressing time and polymer dose were examined in an air pressure plate apparatus to explore their integrated influence on the dewatering of an alum sludge. Results of the investigation demonstrated that dewatering can be enhanced by increases in pressure and time. However, a point is reached at which continued increases in pressure and time offer little benefit. The data also confirmed that polymer affects the rate of water release rather than the extent of dewatering. Increased rates of water release due to increasing polymer dose can be attributed to the aggregation of sludge particles by polymer addition. It was also evident in this study that the initial sludge depth has a major impact on the average cake moisture content at a given dewatering time. It was apparent that once the initial sludge thickness exceeds about 2 cm, the water release follows a fairly similar pattern, which can be represented by a simple empirical model. [Copyright &y& Elsevier]

This paper describes an experimental investigation into the factors which control clogging phenomenon of the filter medium during alum sludge filtration under conditions of excess polymer dosing. Preliminary studies showed that the hydraulic resistance of the filter medium was associated with the amount of polymer trapped, but was not uniquely determined by the quantity of polymer trapped in the filter. Subsequent investigations showed that filter blinding can arise from the interaction of residual polymer and a colloidal fraction. When either of these components was missing, the trapping efficiency of the filter was low. In particular, the study demonstrated that polymer coatings on the filter did not have any significant impact on the hydraulic resistance. Evidence indicated that clogging and polymer trapping was particle size driven, the aggregate size being dependent on the polymer dose. Diagnosis of trends in the filter resistance suggested that they were being influenced by polymer/colloidal solids ratio through its effects on particle size. [Copyright &y& Elsevier]