Dewatered Alum Sludge Research Articles

Operating a two-stage microbial fuel cell-constructed wetland for fuller wastewater treatment and more efficient electricity generation.

By integrating microbial fuel cells (MFCs) into constructed wetlands (CWs) the need and cost of building a reactor are eliminated, while CWs provide the simultaneous redox conditions required for optimum MFC performance. Two single-stage MFC-CWs, with dewatered alum sludge cake as the main wetland medium for enhanced phosphorus removal, were operated to determine the effects of electrode separation and flow regimes on power production and wastewater treatment. When the anode is buried and the cathode is at the air-water interface the system is inhibited by a large ohmic resistance resulting from the increased electrode separation. By placing the cathode directly above the anode and operating the system with simultaneous up-flow into the anode and down-flow into the cathode the ohmic resistance is reduced. The chemical oxygen demand (COD) removal efficiency was, however, reduced to 64% (compared with 79%). A two-stage system was subsequently run for fuller wastewater treatment and increased power production. The results indicate that a two-stage MFC-CW can increase the normalized energy recovery and improve removal efficiencies of COD, total nitrogen, NH4⁺, total phosphorus and reactive phosphorus to 93 ± 1.7%, 85 ± 5.2%, 90 ± 5.4%, 98 ± 5.3% and 99 ± 2.9%, respectively.

Kinetic study of a cationic dye adsorption by dewatered alum sludge

The controlling mechanism of an adsorption process can be assisted by kinetic analysis. The objective of this study was to develop a dye adsorption kinetics model. Remazol blue R dye was used to prepare synthetic textile wastewater. Reusing dewatered alum sludge as the adsorption material to remove dye from synthetic textile wastewater was evaluated in this study. Kinetics study of the dye adsorption was performed by fitting the experimental data into Elovich, pseudo-second order type I, II and intra-particle diffusion kinetic models. The results showed that the adsorption kinetic dye was best described by a pseudo-second order type I kinetic model with R2 of 0·994. The kinetics evaluation indicated that dewatered alum sludge is a good dye adsorption material.

Nitrogen dynamics model for a pilot field-scale novel dewatered alum sludge cake-based constructed wetland system

A model simulating the effluent nitrogen (N) concentration of treated animal farm wastewater in a pilot on-site constructed wetland (CW) system, using dewatered alum sludge cake (DASC) as wetland substrate, is presented. The N-model was developed based on the Structural Thinking Experiential Learning Laboratory with Animation software and is considering organic nitrogen, ammonia nitrogen (NH3) and nitrate nitrogen (NO3-N) as the major forms of nitrogen involved in the transformation chains. Ammonification (AMM), ammonia volatilization, nitrification (NIT), denitrification, plant uptake, plant decaying and uptake of inorganic nitrogen by algae and bacteria were considered in this model. pH, dissolved oxygen, temperature, precipitation, solar radiation and nitrogen concentrations were considered as forcing functions in the model. The model was calibrated by observed data with a reasonable agreement prior to its applications. The simulated effluent detritus nitrogen, NH4-N, NO3-N and TN had a considerably good agreement with the observed results. The mass balance analysis shows that NIT accounts for 65.60%, adsorption (ad) (11.90%), AMM (8.90%) followed by NH4-N (Plants) (5.90%) and NO3-N (Plants) (4.40%). The TN removal was found 52% of the total influent TN in the CW. This study suggested an improved overall performance of a DASC-based CW and efficient N removal from wastewater.

Design of a novel constructed treatment wetland system with consideration of ambient landscape

A ‘fan-shape’ constructed wetland (CW) system is designed to treat domestic wastewater as well as to provide an aesthetically pleasing and environmentally sensitive landscape with ornamental plants for recreation. The system consists of two-stage subsurface horizontal flow CW cells with dewatered alum sludge cakes as the main substrate to ensure the treatment efficiency. The system is located in a new countryside village in Northwest China. The paper presents the design considerations of the CW together with the surrounding landscape to create an integrated CW (ICW). The study attempts to show how the wastewater infrastructure of CW can be an attractive feature in a community; bringing utility and beauty together, and serving needs for education, recreation and habitat conservation, through integrating engineering and landscape design.

Feasibility of Alum Sludge as Phosphate Removal

Alum sludge contained a large portion amount of the aluminum derived from the coagulation process in secondary stage water treatment. Alum sludge is discharge to the landfill and it can affect on disposal management. This study investigates the treatment of wastewater using the low-cost adsorption material and also an innovation in green technology for the preservation of the environment. This finding attempts to determine the effectiveness of dewatered water treatment alum sludge as media to remove pollutant (phosphate) from wastewater. The continuous flow test approach with constant speed allocate is being used in this study. Alum sludge was prepared in 2.36 mm sieve size in dry condition and the initial synthetic water concentration (phosphate solution) was set in increasing order 2.6 mg/L to 30.5 mg/L. The test was monitored over 30 days with constant flow rate. The results indicated removal phosphate in beginning of contact time at 30% - 90%. The maximum percentage removal is 91% - 98% in various condition. The dewatered alum sludge from water treatment plant has great potential as phosphate removal.

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.

STELLA software as a tool for modelling phosphorus removal in a constructed wetland employing dewatered alum sludge as main substrate

A dynamic simulation model was developed for the removal of soluble reactive phosphorus (SRP) from the vertical flow constructed wetlands (VFCW) using a dynamic software program called STELLA (structural thinking, experiential learning laboratory with animation) 9.1.3 to aid in simulating the environmental nature and succession of relationship between interdependent components and processes in the VFCW system. In particular, the VFCW employed dewatered alum sludge as its main substrate to enhance phosphorus (P) immobilization. Although computer modelling of P in treatment wetland has been well studied especially in recent years, there is still a need to develop simple and realistic models that can be used for investigating the dynamics of SRP in VFCWs. The state variables included in the model are dissolved phosphorus (DISP), plant phosphorus (PLAP), detritus phosphorus (DETP), plant biomass (PLBI) and adsorbed phosphorus (ADSP). The major P transformation processes considered in this study were adsorption, plant and microbial uptake and decomposition. The forcing functions which were considered in the model are temperature, radiation, volume of wastewater, P concentration, contact time, flow rate and the adsorbent (i.e., alum sludge). The model results revealed that up to 72% of the SRP can be removed through adsorption process whereas the uptake by plants is about 20% and the remaining processes such as microbial P utilization and decomposition, accounted for 7% SRP removal based on the mass balance calculations. The results obtained indicate that the model can be used to simulate outflow SRP concentration, and it can also be used to estimate the amount of P removed by individual processes in the VFCW using alum-sludge as a substrate.

Performance evaluation and prediction for a pilot two-stage on-site constructed wetland system employing dewatered alum sludge as main substrate

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 11 months. Treatment performance was evaluated and spreadsheet analysis was used to establish correlations between water quality variables. Results showed that removal rates (in g/m 2 d) of 4.6–249.2 for 5 day biochemical oxygen demand (BOD 5), 35.6–502.0 for chemical oxygen demand (COD), 2.5–14.3 for total phosphorus (TP) and 2.7–14.6 for phosphate (PO 4 P) were achieved. Multiple regression analysis showed that effluent BOD 5 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.

Two strategies for improving animal farm wastewater treatment in reed beds

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. Tidal flow operation was employed to enhance oxygen transfer into the system while dewatered alum sludge cake was used to enhance phosphorus (P) removal 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 and this highlights the benefits of using 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 a mean loading rate of 84.6 g/m2.d. The first‐order kinetics constant for BOD5 removal (KBOD, m/d) obtained 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.

Extending the use of dewatered alum sludge as a P-trapping material in effluent purification: Study on two separate water treatment sludges

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 (14.3 mg 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.

Two strategies for phosphorus removal from reject water of municipal wastewater treatment plant using alum sludge

In view of the well recognized need of reject water treatment in MWWTP (municipal wastewater treatment plant), this paper outlines two strategies for P removal from reject water using alum sludge, which is produced as by-product in drinking water treatment plant when aluminium sulphate is used for flocculating raw waters. One strategy is the use of the alum sludge in liquid form for co-conditioning and dewatering with the anaerobically digested activated sludge in MWWTP. The other strategy involves the use of the dewatered alum sludge cakes in a fixed bed for P immobilization from the reject water that refers to the mixture of the supernatant of the sludge thickening process and the supernatant of the anaerobically digested sludge. Experimental trials have demonstrated that the alum sludge can efficiently reduce P level in reject water. The co-conditioning strategy could reduce P from 597-675 mg P/L to 0.14-3.20 mg P/L in the supernatant of the sewage sludge while the organic polymer dosage for the conditioning of the mixed sludges would also be significantly reduced. The second strategy of reject water filtration with alum sludge bed has shown a good performance of P reduction. The alum sludge has P-adsorption capacity of 31 mg-P/g-sludge, which was tested under filtration velocity of 1.0 m/h. The two strategies highlight the beneficial utilization of alum sludge in wastewater treatment process in MWWTP, thus converting the alum sludge as a useful material, rather than a waste for landfill.

Phosphorus removal in laboratory-scale unvegetated vertical subsurface flow constructed wetland systems using alum sludge as main substrate

This research has two eventual goals: (1) To optimize performance of subsurface constructed wetlands for removal of phosphorus (P) (2) To demonstrate that dewatered alum sludge (a by-product), can be reused as a constructed wetland substrate. To achieve these, alum sludge from a water treatment plant was characterized and used as main substrate in four experimental vertical sub-surface flow constructed wetland systems treating dairy farm wastewater. Results show that the alum sludge has suitable hydraulic characteristics (uniformity coefficient = 3.6) for use as a substrate, and in the batch studies, up to 48.6 mg-P was removed by 1 g of the alum sludge at a P concentration of 360 mg-P/l and a dosage of 5 g/l. Results from the experimental systems highlight the significant P removal ability of the alum sludge. However, the inclusion of pea gravel at the infiltrative surface of some of the systems had a negative effect on the P removal performance. Sequential P-fractionation results show that there was no significant increase in the easily extractable P, but for total P, there was significant increase, although this was found to decrease with depth. This study shows that the novel use of dewatered alum sludge can bring about high P removal in vertical subsurface flow constructed wetland systems.

Development of alum sludge-based constructed wetland: An innovative and cost effective system for wastewater treatment

This article describes a research attempt to integrate the dewatered alum sludge, a residual by-product of drinking water treatment process, into a constructed wetland (CW) system for the purpose of enhancing the wastewater treatment performance, thus developing a so called alum sludge-based constructed wetland system. A multi-dimensional research project including the batch tests of phosphorus (P) adsorption onto alum sludge followed by the model CWs trials of single and multi-stage CWs, has been conducted since 2004. It has been successfully demonstrated that the alum sludge-based CW is capable of enhanced and simultaneous removal of P and organic matter (in terms of BOD5 and COD), particularly from medium and high strength wastewater. The sludge cakes act as the carrier for developing biofilm for organics removal and also serve as adsorbent to enhance P immobilization. Batch P-adsorption tests revealed that the alum sludge tested possesses excellent P-adsorption ability of 14.3 mg-P/g.sludge (in dry solids) at pH 7.0 with the adsorption favored at lower pH. The results obtained in a 4-stage treatment wetland system suggest that high removal efficiencies of 90.4% for COD, 88.0% for BOD5, 90.6% for SS, 76.5% for TN and 91.9% for PO4 3 −-P under hydraulic loading of 0.36 m3/m2· d can be achieved. The field demonstration study of this pioneering development is now underway.

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 soluble reactive P (SRP) 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.

Influence of ageing on the structure and phosphate adsorption capacity of dewatered alum sludge

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 23.9 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 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.

Use of dewatered alum sludge as a substrate in reed bed treatment systems for wastewater treatment

In this paper, two laboratory-scale simulated reed beds were investigated for the purpose of assessing the feasibility and effectiveness of using dewatered alum sludge as a possible substrate for wastewater treatment reed bed systems. One horizontal subsurface flow setup and one vertical flow setup were used. The horizontal flow system was planted with Phragmites australis while the vertical flow system was left unplanted. Thus, the latter was more akin to a sand filter system, but was examined with the potential use as a planted vertical reed bed system. The influent source used was farmyard wastewater. It is expected that the present study will provide the basis for long-term and large-scale trials in realizing the concept of integrating “waste” into treatment processes. Results obtained so far have shown that the dewatered alum sludge holds great promise as a low-cost resource media for use in reed bed treatment systems. Appreciable and stable performance was obtained during the continuous operation at high hydraulic, organic and phosphorus loadings. In particular, both wetlands achieved over 90% phosphorus removal, reflecting the significant advantage of this novel approach over conventional reed bed treatment systems. However, extensive research into possible surface clogging and possible release of some substances from the sludge to the treated effluent is necessary to ensure reliability of the system. This will help to make the alum sludge-based reed bed environmentally and economically justifiable.

Dewatered alum sludge: a potential adsorbent for phosphorus removal

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 to 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 3.5 mg-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.

Involvement of Gypsum (CaSO4 · 2H2O) in Water Treatment Sludge Dewatering: A Potential Benefit in Disposal and Reuse

This research assessed the use of gypsum (CaSO4 · 2H2O) as a skeleton builder for sludge dewatering since polymer conditioning of sludge affected only the rate of water release, not the extent of dewatering. The use of gypsum as a physical conditioner, in association with a polymer, could improve sludge filterability. More significantly, gypsum serves as a skeleton builder, forming a permeable and rigid lattice structure that can remain porous under high positive pressure during the compression step after the cake growth of the filtration, thereby maintaining the size of the micro‐passages through which water is expressed. Experiments using a high pressure cell apparatus showed that a further decrease of two to seven percent of the equilibrium moisture content of the sludge cake was achieved, for sludge thicknesses for dewatering of 1 to 10 cm, by the addition of gypsum with 60% of the original sludge solids when compared to the single polymer conditioning. The importance of the addition of gypsum in alum sludge dewatering is not only the improvement in the extent of dewatering, but also the potential application of transforming dewatered alum sludge from “waste” for landfill to useful “fertilizer” or to be used as a filter medium/adsorbent for wastewater treatment engineering.

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 SO 4 2− and Cl −, onto alum sludge reveal that alum sludge can selectively adsorb phosphate ions. The insignificant effect of SO 4 2− 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 SO 4 2−, 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 PO 4 3− and total aluminium concentration in solution indicate that chemical reaction and precipitation are other mechanisms of phosphate removal.