Alum Sludge Conditioning Research Articles

Dewatered Sludge Decorated with Nanoparticles for Alum Sludge Conditioning towards the Concept of "End-of-Waste".

The circular economy concept is leading environmental engineering in the search for "End-of-Waste" criteria. Untreated waste residue results from drinking water treatment plants, causing severe environmental issues, and its reuse is essential. In this regard, this investigation introduces the beneficial reuses of alum sludge cake to close the loop between sludge waste generation and reuse. Considering alum sludge as a resource for dewatering instead of its categorization as a waste reflects an "End-of-Waste" approach. Alum sludge cake was thermally calcined at 400 °C and named thermally treated alum sludge cake (TAS-cake). In this study, TAS-cake decorated with magnetite with a percent weight of 5 to 1%, respectively, was labeled as TAS-cake@Fe-(5-1). X-ray diffraction (XRD) and morphologies were applied to characterize the hybrid composite. A Fenton-based hybrid composite was applied to extrude water from alum sludge for 7 min of conditioning time. Furthermore, the factorial design based on response surface methodology (RSM) was applied to optimize the operational variables. TAS-cake@Fe-(5-1) and hydrogen peroxide revealed 1.2 g/L and 740 mg/L doses at pH 3.0, showing pronounced performance and revealing the highest capillary suction time (CST) reduction, which reached 53%. A temperature increase also showed a pronounced enhancement effect on the sludge dewaterability that reached 72% when 55 °C was applied. Thus, such a novel conditioner is a promising candidate for alum sludge conditioning.

Alum sludge conditioning with ferrous iron/peroxymonosulfate oxidation: Characterization and mechanism

Alum sludge produced by drinking water plants needs to be conditioned and dewatered before final disposal. In this study, a novel ferrous iron/peroxymonosulfate (PMS) oxidation process was employed to enhance alum sludge dewaterability The effect of oxidative sulfate radicals generated by Fe2+ activated HSO5− on alum sludge was studied. The results showed that the optimal conditioning conditions for addition of Fe2+ and PMS were 0.5 g/g and 0.1 g/g TSS, respectively. Meanwhile, the capillary suction time (CST) and specific resistance to filtration (SRF) of alum sludge was reduced by 66% and 88%. Also found was that the absolute value of the zeta potential increased and the particle size decreased in alum sludge after Fe2+-PMS conditioning, which indicated that oxidative sulfate radicals destroyed the floc structure of alum sludge and smaller particles were generated. At the same time, the water contained in sludge flocs was released and enhanced sludge dewaterability, while leaching of aluminum ions also characterized decomposition of alum sludge.

Pilot Scale Evaluation of Pellet Fluidized Bed Process for the Conditioning of Alum Sludge

As a burgeoning technology based on conventional clarifier technology, pellet fluidized bed (PFB) technology has been widely applied in kinds of high SS water treatment process. In this paper, PFB process was used to thicken the alum sludge in a water plant in south China with scale of 1.0~2.5m3/h. The experimental results showed that, increasing flocculent (PAM) dosage could decrease outlet turbidity, and average up pellets settling behavior. Under the experimental condition, there exist negatively linear relationship between process maximum flow rate which ranged from 1.6m3/h to 2.2 m3/h and raw sludge concentration. Moreover, because of the improvement of pH environment and flocs chemical structure, additional lime dosage would enhance maximum surface loading and save PAM dosage. The pilot scale experiment proved that by applying PFB, alum sludge conditioning could achieve satisfied results characterised by high surface loading, low outlet turbidity, and high concentration thicken sludge with fine dewaterability.

FENTON AND FENTON-LIKE AOPs FOR ALUM SLUDGE CONDITIONING: EFFECTIVENESS COMPARISON WITH DIFFERENT Fe2+ AND Fe3+ SALTS

Currently, organic polymers are adopted in alum sludge (aluminum-coagulated drinking water treatment sludge) conditioning. However, there are important concerns regarding the use of these polymers because of the unknown and long-term effects of the potential release of excess polymer to the surrounding environment when the sludge is landfilled. Therefore, as an initial action, this study aimed at investigating alternative chemical conditioning methods and focused mainly on exploiting Fenton (Fe2+/H2O2) and Fenton-like (Fe3+/H2O2) reagents as the conditioner. Experiments have been conducted to test the effectiveness of Fenton's reagent (containing the ferrous salts of chloride, sulfate, or oxalate), Fenton-like reagent (containing ferric salts of chloride and sulfate), and the coagulation method using FeCl3 for alum sludge conditioning at constant hydrogen peroxide and iron salt concentrations of 125 and 20 mg/g DS (dry solids), respectively. The effectiveness on dewaterability of the alum sludge demonstrated that the maximum reduction (%) of SRF (specific resistance to filtration) and CST (capillary suction time) of 74% and 47%, respectively, can be obtained when Fenton's reagent was adopted for sludge conditioning. Such reduction of 64% for SRF and 38% for CST can be achieved when Fenton-like reagents were applied.

Exploitation of Fenton and Fenton-like reagents as alternative conditioners for alum sludge conditioning

The use of Fenton's reagent (Fe2+/H2O2) and Fenton-like reagents containing transition metals of Cu(II), Zn(II), Co(II), and Mn(II) for an alum sludge conditioning to improve its dewaterability was investigated. The results obtained were compared with those obtained from conditioning the same alum sludge using cationic and anionic polymers. Experimental results show that Fenton's reagent was the best among the Fenton and Fenton-like reagents for the alum sludge conditioning. A considerable effectiveness of capillary suction time (CST) reduction efficiency of 47% can be achieved under test conditions of Fe2+/H2O2 = 20/125 mg/g DS (dry solid) and pH 6.0. The observation of floc-like particles after Fenton's reagent conditioning of alum sludge suggested that the mechanism of Fenton's reagent conditioning was different from that of polymer conditioning. In spite of the lower efficiency in the CST reduction of Fenton's reagent in alum sludge conditioning compared to that of polymer conditioning, Fenton's reagent offers a more environmentally safe option. This study provided an example of proactive treatment engineering, which is aimed at seeking a safe alternative to the use of polymers in sludge conditioning towards achieving a more sustainable sludge management strategy.

Optimization of alum sludge conditioning by microwave process

Optimization of alum sludge conditioning by microwave process

Polymer conditioning of alum sludge and discrepancies between estimates of the optimum dosage

The paper outlines the effects of polymer conditioning on alum sludge properties, such as floc size, density, fractal dimension (DF) and rheological properties. Experimental results demonstrate that polymer conditioning of alum sludge leads to: larger floc size with a plateau reached in higher doses; higher densities associated with higher doses; increased degree of compactness; and an initial decrease followed by an increase of supernatant viscosity with continued increase in polymer dose. The secondary focus of this paper dwells on a comparison of the estimates of optimum dose using different criteria that emanate from established dewatering tests such as CST, SRF, liquid phase viscosity and modified SRF as well as a simple settlement test in terms of CML30. Alum sludge was derived from a water works treating coloured, low-turbidity raw waters.

Correlations between floc physical properties and optimum polymer dosage in alum sludge conditioning and dewatering

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.

Conditioning of alum sludge with polymer and gypsum

In this study, gypsum was introduced into alum sludge as a skeleton builder in combination with a polymer. The selection of gypsum lies in its common use as an amendment for ameliorating alkaline soils and may enhance the potential disposal of alum sludge to land. Preliminary work describes the impact of gypsum on the net sludge solids yield ( Y N), a factor which is used to express sludge filterability. Experiments demonstrated that gypsum could be used in association with a polymer to improve sludge filterability. The purpose of the skeleton builder is to form a permeable and rigid lattice structure that can remain porous under high pressure. By examining the polymer residual in the bulk solution and comparing data between the cases of gypsum and glass-microsphere (as a non-shrinking skeletal material) it was evident that the gypsum possesses a polymer demand indicating an interaction between them.

Effect of surfactant on alum sludge conditioning and dewaterability

Sludge disposal has become a new challenge for the Taiwan government due to the increasing demand for better quality and greater quantity of water. In some water treatment plants, surfactant has been applied in the flotation process to improve its performance, which suggests the use of surfactant in sludge conditioning. In this study, effects of surfactants on the conditioning of the alum sludge collected from Feng-Yuan Water Treatment Plant were investigated. Surfactants of various charges, namely CTAB and SDS, were added to sludge samples in various amounts, and their effects on sludge dewaterability were evaluated. Surfactants were also added with either cationic or anionic polymers to better understand their effects on the mechanism of sludge conditioning and the feasibility as coagulant aid.Experimental results indicate that applying surfactants alone in sludge system decrease the filterability of sludge, but increase the sludge dewatering rate at optimum dosage. Cationic surfactant was proven possible as conditioning aid for the cationic polymer. The order of surfactant and polymer addition is the key to additive function. On the other hand, when the polymer of opposite charge was added with the surfactant, co-precipitation occurred which resulted in decreased filterability and dewaterability.

A new technique for monitoring alum sludge conditioning

A technique based on measurements of fluctuations in the intensity of light transmitted through a flowing sludge suspension was used to evaluate polymer performance in alum sludge conditioning. The ratio of the r.m.s. of the fluctuations to the average transmitted light intensity exhibits a well-defined response, usually a substantial increase, to sludge particle aggregation. This aggregation reflects the improvement in sludge filterability as also indicated by concurrent CST measurements. Five polymers, cationic, anionic and nonionic were used in conditioning the sludge. Tests were conducted using a mixer set at 700 rpm with a corresponding velocity gradient of 1900 s −1. The technique was shown to give a very rapid convenient indication of the conditioning effect of polymeric flocculants. It could be very easily adapted to online applications.