Urban Institute Ireland Research Collection

In this study, alum sludge was introduced into co-conditioning and dewatering with an anaerobic digested activated sludge to examine the role of the alum sludge in improving the dewaterbility of the mixed sludge and also in immobilizing phosphorus in the reject water. Experiments have demonstrated that the optimal mix ratio for the two sludges is 2:1 (anaerobic digested sludge: alum sludge; volume basis), and this can bring about 99% phosphorus reduction in the reject water through the adsorption of phosphorus by Al in the sludge. The phosphorus loading in wastewater treatment plants is itself derived from the recycling of reject water during the wastewater treatment process. Consequently, this co-conditioning and dewatering strategy can achieve a significant reduction in phosphorus loading in wastewater treatment plants. In addition, the use of the alum sludge can beneficially enhance the dewaterbility of the resultant mixed sludge by decreasing both the SRF and the CST, due to the alum sludge acting as a skeleton builder. Experiments have also demonstrated that the optimal polymer (Superfloc C2260) dose for the anaerobic digested sludge was 120 mg/l while the optimal dose for the mixed sludge (mix ratio 2:1) was 15 mg/l, highlighting a huge saving in polymer addition. Therefore, from the technical perspective, the co-conditioning and dewatering strategy can be viewed as a “win-win” situation. However, for its full-scale application, integrated cost-effective analysis of process capabilities, sludge transport, increased cake disposal, additional administration, polymer saving etc. should be factored in.

Alum sludge refers to the by-product from the processing of drinking water in Water Treatment Works. In this study, groups of batch experiments were designed to identify the characteristics of dewatered alum sludge for phosphorus adsorption. Air-dried alum sludge (moisture content 10.2%), which was collected from a Water Treatment Works in Dublin, was subjected for artificial P-rich wastewater adsorption tests using KH2PO4 as a model P source. Adsorption behaviours were investigated as a function of amount and particle size of alum sludge; pH of solution; and adsorption time. The results have shown that pH plays a major role not only in the adsorption process but also in the adsorption capacity. With regard to adsorption capacity, this study reveals the Langmuir adsorption isotherm being the best fit with experimental data (R2=0.98-0.99). The maximum adsorption capacities range from 0.7 to 3.5mg-P/g when the pH of the synthetic P solution was varied from 9.0 to 4.3, accordingly. The outcome of this study indicated that alum sludge is suitable for use as an adsorbent for removal of phosphate from wastewater.

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.

The generation of alum sludge from drinking water purification process remains inevitable when aluminium sulphate is used as primary coagulant for raw water coagulation. Sustainable managing such the sludge becomes an increasing concern in water industry. Its beneficial reuse is therefore highly desirable and has attracted considerable research efforts. In view of the novel development of alum sludge as a value-added raw material for beneficial reuse for wastewater treatment, this study examined the maximum phosphorus-adsorption capacity of two dewatered alum sludges sampled from two largest water treatment works in Dublin, Ireland. The objective lies in clarifying the change of alum sludge characteristics and its P-adsorption capacity over the location of the alum sludge produced and the raw water being treated. Experiments have demonstrated that the two alum sludges have the similar P adsorption capacity (14.3mg P/g sludge for Ballymore-Eustace sludge and 13.1 mg P/g sludge for Leixlip sludge at pH 7.0). However, the study supports that alum sludge beneficial reuse as a low cost adsorbent for P immobilization should study its P-adsorption capacity before any decision of large application is made since the raw water quality will affect the sludge characteristics and therefore influence its adsorption ability.

As a biomass material, bone char was investigated for the feasibility to be used as a cost-effective biosorbent for fluoride removal from drinking water in groundwater environment. Based on the batch tests with natural tourmalin and active alumina being the reference adsorbents, BF (referring to bone char) has demonstrated a higher fluoride adsorption capacity. This capacity was found being increased with the increase of fluoride concentration. Furthermore, BF based column adsorption experiments indicated that the fluoride removal could be significantly affected by flow rate and bed height. A mass transfer model developed in this study can be used to optimize the bed configuration and operation parameters. Experimental results and predicted data by the model have shown a good consistent. A full-scale BF fixed-bed to treat fluoride-containing groundwater in Northeast China has been successfully operated since 2002.

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.

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 23.9 mg-P g-1-sludge at pH 4.3, 14.3 to 14.9 mg-P g-1-sludge at pH 7.0 and 0.9 to 1.1 mg-P g-1-sludge at pH 9.0, respectively, indicating marginal effect of ageing time on such sludge's ability to adsorb phosphate. This result seems conflict with other studies reported in the literature. To reveal such, series of investigations including physicochemical characterization, morphological structure, BET surface area and porous structure of the aged sludge were carried out. All the results conclusively show that ageing time has insignificant effect on the structure and properties of the dewatered alum sludge and thus the phosphate adsorption capacity of the alum sludge remains insignificant change during the ageing.

This study assessed the potential reuse of an aluminium coagulated drinking–water treatment sludge (Al–DWTS) as a main substrate in constructed wetland to replace soil for the treatment of P-enriched wastewater. The adsorption isotherm and kinetics of phosphorus (P) removal from high-P solution by Al–DWTS and a local soil from Bailieborough, Ireland, were studied and compared under laboratory conditions. Data of P adsorption were well fitted to the Langmuir and the Freundlich isotherms but the Freundlich isotherm had a higher correlation coefficient. The maximum P adsorption capacity of the Al–DWTS and the soil was 39.4 mg P mg–1 and 9.5 mg P mg–1, respectively, at conditions of pH of 4.0 and temperature of 23 °C. Kinetics studies show that adsorption in both cases followed pseudo-second-order kinetics. The fact that the Al–DWTS exhibited a significantly higher P adsorption capacity at high–P solution compared with the soil suggests that Al–DWTS can be a “novel–waste” bioadsorbent with promising application in wastewater treatment engineering, such as constructed wetland systems.

The aluminium content in dewatered aluminium-coagulated water treatment residual (DAC-WTR) can lead to a high phosphorus (P) removal capacity. Therefore, DAC-WTR has been used as adsorbent/soil amendment to remove P in several studies, focusing mostly on orthophosphates (ortho-P). This study is concerned with extending such reuse of DAC-WTR to remove P using a condensed phosphate as the model P source. Using a 48-hr equilibration time and a 1.18mm (mean particle size); (1) P removal was found to increase with increasing DAC-WTR dosage, but specific uptake of P per mass of DAC-WTR was decreased (2) A maximum adsorption capacity of 4.52mg-P/g of DAC-WTR was obtained at a pH of 4.0. In the continuous flow test, P removal efficiency decreased from 90 to 30% when loading was increased from 3.9 to 16.5g-P/m2.d. An average 45% removal efficiency was obtained after an intentional P loading surge. At the end of the continuous flow test, an operating removal capacity of 2.66 mg-P/g of DAC-WTR was determined which was 83.3% of the adsorption maxima obtained in the batch tests. There was no excessive loss of solids during the continuous flow test and aluminium content in the effluent remained below 0.1mg-Al3+/l. These results have demonstrated that dewatered DAC-WTR can further be used as a low-cost adsorbent media for condensed phosphate removal.

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.

This study investigated the glyphosate adsorption by water treatment residual (termed as alum sludge) in dewatered form (DAS) and liquid form (LAS). Batch adsorption tests were carried out with DAS at different pH, particle size and DAS mass. Standard jar tests were conducted with LAS at two different concentrations (3 g/l and 5 g/l) for glyphosate adsorption. Thereafter, the glyphosate-enriched LAS (after adsorption tests) was subjected to sludge conditioning procedure with polymer LT25 as conditioner to explore any possible further glyphosate reduction. The results indicate that alum sludge has the high adsorption capacity of 85.9 mg/g for DAS and 113.6 mg/g for LAS. This demonstrated the potential of the alum sludge to be an efficient and cost-effective adsorbent for glyphosate removal in comparison with other adsorbents, such as soils, humic substances, clay minerals, and layered double hydroxides (LDH). The polymer conditioning of the glyphosate-enriched LAS cannot bring about the further glyphosate reduction in the supernatant of the dewatered LAS. Overall, this study promotes the beneficial reuse of alum sludge in wide range of pollutant control in environmental engineering.

The purpose of this study is to optimize adsorption conditions of powdered alum sludge (PAS) as low-cost adsorbent for the removal of three P-species (ortho-P, poly-P and organic-P) from wastewater using the response surface methodology (RSM). Initially, RSM in the basis of a three-variable Box-Behnken design was used to determine the effect of pH (from 4 to 7), PAS mass (from 0.1 to 0.5 g) and PAS particle size (from 125 to 420 μm) on the response levels (removal efficiencies of the three P-species). Three response surface quadratic models in terms of three factors were then obtained from an analysis of the experimental data using a SAS computer package. Thereafter, the effect of each of the parameters on P removal for each of the three species was examined using the three-dimensional response surface. All three parameters (pH, PAS mass and PAS particle size) had a significant effect on the removal of each of the P species. Finally, optimal conditions for P species removal were determined at which the P-removals of 99.8 % (for ortho-P), 94.9 % (for poly-P) and 94.8 % (for organic-P) were achieved, respectively. The results derived from the verification experiments agreed with that predicted by the models, confirming the suitability of the established models and the success of RSM in optimizing the PAS adsorption conditions.

The adsorption equilibrium of a wide range of phosphorus species by an aluminium-based water treatment sludge (Al-WTS) was examined in this study. Four kinds of adsorption-isotherm models, namely Langmuir, Freundlich, Temkin and Dubinin-Radushkevich, were used to fit the adsorption equilibrium data. In order to optimise the adsorption-isotherm model, correlation coefficient (R2) and four error functions were employed to facilitate the evaluation of fitting accuracy. Experiments have demonstrated that the Al-WTS may be an excellent raw material to adsorb P in polluted aqueous environment with adsorption ability in the order of KH2PO4 (ortho-P) > Na(PO3)6 (poly-P) > C10H14N5O7P·H2O (organic-P). More importantly, this study provides an entire comparison of the four isotherms in describing the P adsorption behaviour. By considering both the standard least-square based R2 and the results of four error functions analysis, this study reveals that the Freundlich isotherm appears to be the best model to fit the experimental equilibrium data. Langmuir and Temkin isotherms are also good models in current experimental conditions while Dubinin-Radushkevich isotherm poorly described the adsorption behaviour. The error analysis in this study provides vital evidence to reflect its role in facilitating the optimisation in adsorption isotherm study. Obviously, R2 seems inadequate in optimising multi-isotherm models due to its inherent bias resulting from the least-squares linearisation.

Effective management of the industrial waste requires a sustainable approach that maximizes its value of reuse/recycle for other industrial demands and the environment needs. This paper aims in exploring the potential of the intended purposes in the newly developed dewatered aluminum-water treatment sludge (Al-WTS) based engineered wetland (EW) for wastewater treatment. Due to the low energy requirement and aesthetical appearance EW is seen as a ‘green’ wastewater treatment technique worldwide for a wide variety of wastewater treatment. The Al-WTS based EW developed at University College Dublin, Ireland, represents the latest initiative at using engineering ingenuity to further improve EWs performance. This paper summarizes the background of development and the results derived from different phases of the development of Al-WTS based EW.