Polyaluminium Chloride Sludge Research Articles

Adsorption of fluoride by using sodium alginate coated poly-aluminium chloride (PAC) sludge: preparation, characterisation and mechanism

ABSTRACT Poly-aluminium chloride (PAC) sludge is a waste product created during drinking water treatment, usually generated in large quantities and typically landfilled. More attention must be directed to environmental-friendly management and economically sustainable of Al-based sludge. In this work, a low-cost and environmental-friendly adsorbent prepared by sodium alginate coated PAC sludge (SPS) was investigated for fluoride removal. Basic preparing parameters including heating temperature (200–800°C), sodium alginate concentration (0.5–5 wt%), particle size (1–2 mm, 2–3 mm, 3–4 mm) and operating parameters including dosage (1–14 g/L), solution pH (4–11), temperature (10–35°C), co-existing anions (NO3 −, Cl−, SO4 2-, PO4 3-) were examined to evaluate the optimum defluoridation capacity. The prepared SPS adsorbents reached a high removal efficiency of 95.6% with initial fluoride concentration of 10 mg/L, dose of 8 g/L, contact time of 24 h, pH value of 7 and temperature of 10°C. The kinetic study indicated that fluoride adsorption followed the pseudo-second-order kinetics well (R2 = 0.9942), and adsorption isotherms can be well described by Freundlich model (R2 = 0.9952). Thermodynamic studies showed the fluoride adsorption was spontaneous and exothermic. The elements and functional groups of SPS adsorbents were analysed by using EDS and FTIR, respectively. The adsorption mechanism involved physisorption, ligand-exchange and electrostatic attraction. According to N2 adsorption–desorption isotherm, the SPS was mesoporous material which facilitated the adsorption of fluoride ions. Also, aluminium presented in form of Al-OH in SPS adsorbents had significant contribution in fluoride adsorption. The concentration of the residual aluminium ions was 4.48 × 10−3 mg/L which is lower than the China Drinking Water Standard. The encouraging results of this preliminary study indicated that SPS is an environmental-friendly and cost-effective treatment option for groundwater with fluoride pollution.

Phosphorus removal by adsorbent based on poly-aluminum chloride sludge

Phosphorus adsorption tests were carried out using poly-aluminum chloride sludge (PACS), which was collected from a water treatment plant in Nanjing. The amount of phosphorus adsorbed by PACS increased quickly within the first hour and reached equilibrium after about 48 h. The adsorption behavior of PACS for phosphorus is consistent with the Langmuir adsorption isotherm equation (R2 > 0.99) and parallel first-order kinetic equation (R2 > 0.98). With the increase of the PACS concentration, the adsorption capacity of PACS for phosphorus decreased, and the removal rate increased. The results of batch tests showed that the adsorption capacities of PACS for phosphorus ranged from 1.64 to 1.13 mg/g when the pH value varied from 4 to 10. However, the adsorption capacity of PACS was not evidently influenced by temperature. In comparison with the ion exchange resin, the adsorption capacity of PACS was barely inhibited by competitive ions, such as SO42−, NO3−, and Cl−. The PACS surface after adsorption became smooth, and the vibration peaks of Al–O and Al–OH shifted. Both HCl and NaOH have a strong desorption effect on PACS after adsorption saturation, and with higher concentrations of HCl and NaOH, the desorption effect was stronger. Results of column adsorption experiments showed that with lower phosphorus and hydraulic loads, the adsorption column took longer to reach saturation. This indicated that PACS could be used as an efficient material for removal of phosphorus from water. This study provides a new treatment method with PACS.

Alkaline fermentation promotes organics and phosphorus recovery from polyaluminum chloride-enhanced primary sedimentation sludge

In this study, alkaline fermentation was applied to promote organics and P recovery from polyaluminum chloride (PACl)-enhanced primary sedimentation sludge. Coagulant results demonstrated that the optimum PACl dosage of 100 mg/L resulted in the effective concentration of 73% of organic matter and 90% of P from wastewater into sludge. Batch fermentation results highlighted the ability of alkaline fermentation in improving the biodegradability of PACl sludge. More specifically, at pH 11, 43.3% of soluble organics and 36.49% of P were released to the fermentation supernatant. Furthermore, P fractionation fermented sludge results revealed that partial Al-P dissolution and organic phosphorus hydrolysis were the main drivers of the released P. Finally, at pH 11, 85% of P was recovered as magnesium ammonium phosphate from the fermentation supernatant at the 2:1 Mg/P molar ratio. In conclusion, 24.9% of organics and 27.9% of P from raw wastewater were converted to valuable products via alkaline fermentation.

Use of waste sludge generated from water defluoridation plant as partial substitute for fine aggregates in mortars: microstructural characterization and compressive strength

In the present study, sludge produced from the continuous defluoridation set-up was used as partial replacement for fine aggregates in mortar making. Aluminium sulphate (alum) and polyaluminium chloride (PACl) were used as coagulants for fluoride removal and mortar cubes with size of 50 mm × 50 mm × 50 mm were prepared with alum and PACl sludge in different proportions, i.e. 0%, 1%, 2%, 3%, 4% and 5%. The compressive strength tests were conducted and it was observed that the strength of mortar with 1% replacement increased by 2.5% for alum sludge and 6% for PACl sludge and the compressive strength showed satisfactory values up to 3% sludge replacement for alum and PACl sludge. The impact of partially replacing alum and PACl sludge on the strength of mortars regarding calcium silicate hydrate gel, silica and other hydration products was studied. Toxic Characteristics Leaching Procedure was performed for the mortars and aluminium concentration was within the permissible limits of 0.2 ppm. The results suggested that the reuse of alum and PACl sludges can lead to new paths in reducing the deterioration of the ecosystem because of waste disposal.

Mechanistic insights into nature of complexation between aluminum and phosphates in polyaluminum chloride treated sludge for sustainable phosphorus recovery

Efficiency of phosphorus recovery from polyaluminum chloride sludge is determined by chemical interactions between Al and P. Chemical structure of Al–P complex and their binding mechanisms in the PAC sludge were investigated with spectroscopy and chemical fractionation. More than 98% of the P was bound with Al, out of which 70% was strongly bound. The ATR-FTIR analysis indicates that the majority of the P formed inner sphere complex with Al through ligand exchange. The availability of highly protonated surface for P sorption at low pH also supports the formation of Al–P outer sphere complex.

Influence of sludge characteristics on coagulant recovery from water treatment sludge: a preliminary study

This study investigated the effect of raw water quality and coagulant type and dosage on the efficiency of aluminium recovery from water treatment sludge by acidification process. One of the features of this study is to prioritise several factors affecting aluminium recovery using demonstrating experiments and analysing the result using model. The previous studies comparing the aluminium recovery from PACl and alum sludge had collected the sludge from treatment plants treating different source water. However, this study compares aluminium recovery from PACl and alum sludge obtained from treating same source water. Water treatment sludge was prepared in laboratory by coagulating raw water with different inorganic and organic contents using aluminium sulphate (alum) and polyaluminium chloride (PACl) as coagulants. The effect of the different factors on the aluminium recovery efficiency was evaluated using a 23 full factorial experimental design. The aluminium recovery efficiency was higher for PACl sludge compared to alum sludge with recovery ranging from 62.5 to 74.5 % for alum sludge and from 70.7 to 84.0 % for PACl sludge. At higher concentrations of organic matter and turbidity in the raw water, lower aluminium recovery efficiency was observed for both the sludges. The study thus shows the important effects of raw water quality and coagulant type and dose on the recovery process.

Coagulant recovery from water treatment plant sludge and reuse in post-treatment of UASB reactor effluent treating municipal wastewater.

In the present study, feasibility of recovering the coagulant from water treatment plant sludge with sulphuric acid and reusing it in post-treatment of upflow anaerobic sludge blanket (UASB) reactor effluent treating municipal wastewater were studied. The optimum conditions for coagulant recovery from water treatment plant sludge were investigated using response surface methodology (RSM). Sludge obtained from plants that use polyaluminium chloride (PACl) and alum coagulant was utilised for the study. Effect of three variables, pH, solid content and mixing time was studied using a Box-Behnken statistical experimental design. RSM model was developed based on the experimental aluminium recovery, and the response plots were developed. Results of the study showed significant effects of all the three variables and their interactions in the recovery process. The optimum aluminium recovery of 73.26 and 62.73 % from PACl sludge and alum sludge, respectively, was obtained at pH of 2.0, solid content of 0.5 % and mixing time of 30 min. The recovered coagulant solution had elevated concentrations of certain metals and chemical oxygen demand (COD) which raised concern about its reuse potential in water treatment. Hence, the coagulant recovered from PACl sludge was reused as coagulant for post-treatment of UASB reactor effluent treating municipal wastewater. The recovered coagulant gave 71 % COD, 80 % turbidity, 89 % phosphate, 77 % suspended solids and 99.5 % total coliform removal at 25 mg Al/L. Fresh PACl also gave similar performance but at higher dose of 40 mg Al/L. The results suggest that coagulant can be recovered from water treatment plant sludge and can be used to treat UASB reactor effluent treating municipal wastewater which can reduce the consumption of fresh coagulant in wastewater treatment.

Reusing spent polyaluminum chloride sludge as adsorbent for phosphate removal from secondary wastewater effluent

Abstract This study explored the reuse potential of spent polyaluminum chloride (PAC) sludge as an adsorbent for removing phosphate from secondary wastewater effluent. The adsorption isotherm and kinetics were examined in batch experiments. The effect of temperature, pH, and foreign anions on phosphate adsorption was also investigated. Additionally, continuous column adsorption was employed to evaluate the applicability of the bed-depth-service-time (BDST) model. Experimental results reveal that the adsorption of phosphate onto PAC sludge was rapid in the preliminary 30 min and the adsorption behavior followed a pseudo-second-order model. Langmuir isotherm correlated the experimental data better than Freundlich isotherm and the maximum value of adsorbed phosphate (q m) was 2.21 mg P/g SS. Besides, the phosphate adsorption was favored at higher temperature and lower pH and was hardly interfered by the competing anions. Furthermore, the process of phosphate adsorption was spontaneous and endothermic in terms of the thermodynamic parameters, ΔH 0, ΔS 0, and ΔG 0. Finally, the BDST model was appropriate to describe the adsorption of phosphate by PAC sludge in the column mode and could be successfully used in predicting the breakthrough and exhaustion time.

Response surface optimization of acid red 119 dye from simulated wastewater using Al based waterworks sludge and polyaluminium chloride as coagulant

In this research, the performance of Polyaluminium Chloride (PAC) and Polyaluminium Chloride sludge (PACS) as coagulants for acid red 119 (AR119) dye removal from aqueous solutions were compared. The sample of PACS was collected from “Baba Sheikh Ali” water treatment plant (Isfahan, Iran) where PAC is used as a coagulant in the coagulation/flocculation process. A response surface methodology was applied to evaluate the simple and combined effects of the operating variables including initial pH, coagulant dosage and initial dye concentration and to optimize the operating conditions of the treatment process. Results reveal that the optimal conditions for dye removal were initial pH 3.42, coagulant dosage of 4.55 g dried PACS/L and initial dye concentration of 140 mg/L for PACS, while the optimal initial pH, coagulant dosage and initial dye concentration for PAC were 3.8, 57 mg/L and 140 mg/L, respectively. Under these optimal values of process parameters, the dye removal efficiency of 94.1% and 95.25% was observed for PACS and PAC, respectively. Although lower amount of PAC in comparison with PACS was needed for specific dye removal, the reuse of PACS as a low-cost material can offer some advantages such as high efficiency for AR119 dye removal and economic savings on overall water and wastewater treatment plant operation costs.

A comparison study on Acid Red 119 dye removal using two different types of waterworks sludge

This study aims to compare the performance of two waterworks sludge samples, ferric chloride sludge (FCS) and polyaluminium chloride sludge (PACS), as coagulants to remove Acid Red 119 (AR119) dye from aqueous solution. A series of batch experiments were performed to investigate the effect of initial pH, coagulant dosage and initial dye concentration on coagulation/flocculation process efficiency. Results showed that the dye removal was strongly pH-dependent and followed the same trend for both coagulants, increasing steadily with decreasing initial pH in the range of 3-12. With the increase of coagulant dosage, the dye removal efficiency increased and no re-stabilization phenomenon was observed. However, the coagulant dosage needed for the maximum dye removal efficiency was much lower for FCS (150 mg dried sludge/L) in compare with PACS (5.5 g dried sludge/L). It seems that both charge neutralization and sweep flocculation mechanisms were involved in removal of AR119 using FCS and PACS. With the increase of initial dye concentration, Q (the amount of the removed dye per unit mass of coagulant) steadily increased and reached to a maximum value of 0.96 mg dye/mg sludge and 0.029 mg dye/mg sludge for FCS and PACS, respectively. FCS was more effective than PACS for AR119 dye removal due to the higher amount of dye removed per unit mass of sludge.

Leito de drenagem: sistema natural para redução de volume de lodo de estação de tratamento de água

As Estações de Tratamento de Água (ETAs) tem funcionamento semelhante a uma indústria e podem em diversas etapas gerar resíduos que, na maioria das ETAs, são lançados nos corpos d’água sem tratamento. Neste trabalho avaliou-se o desempenho de Leitos de Drenagem, para o desaguamento de lodo, provenientes de ETAs de ciclo completo que empregam sulfato de alumínio e cloreto de polialumínio (PACl), como coagulantes. Analisou-se as características, a drenagem e secagem dos amostras de lodo e característica do drenado. Os Leitos de Drenagem mostraram-se eficientes para desaguamento e redução de volume de lodo de ETA, de forma natural, sem consumo de energia ou adição de produtos químicos. Obteve-se, aos sete dias, reduções da ordem de 87 % em volume para os lodos de PACl e 83 % para o lodo de Sulfato de Alumínio e teor de sólidos totais 28% e 31% respectivamente.