Alternative low-cost adsorbent for water and wastewater decontamination derived from eggshellwaste: an overview

As the current global trend towards more stringent environmental standards, technical applicability and cost-effectiveness became key factors in the selection of adsorbents for water and wastewater treatment. Recently, various low-cost adsorbents derived from agricultural waste, industrial by-products or natural materials, have been intensively investigated. In this respect, the eggshells from egg-breaking operations constitute significant waste disposal problems for the food industry, so the development of value-added by-products from this waste is to be welcomed. The egg processing industry is very competitive, with low profit margins due to global competition and cheap imports. Additionally, the costs associated with the egg shell disposal (mainly on landfill sites) are significant, and expected to continue increasing as landfill taxes increase. The aim of the present review is to provide an overview on the development of low-cost adsorbents derived from eggshell by-products

Enzymatic treatment effects on dewaterability of anaerobically digested biosolids-II: laboratory characterizations of drainability and filterability

This paper provides an analysis of different measurements and derived parameters that may be used to characterize drainability and filterability dynamics. To better simulate the phenomena of gravity drainage and expression dewatering, specific devices and procedures were used in bench-scale conditioning and dewatering experiments. The setup included a plow simulator kit for drainage simulation and a mechanical dewatering unit, namely, the Crown Press (TM), which simulates full-scale belt filter press dewatering. The effects of enzyme product additions prior to polymer conditioning of biosolids samples were investigated. The results showed that enzyme additions enhanced the drainability of the biosolids samples and this positively affected filterability of the samples in the press unit. According to these results, enzyme product addition for biosolids samples with polymer conditioning seems a promising new method of enhancing the performance of mechanical dewatering units in the future. (c) 2004 Elsevier Ltd. All rights reserved

Dual polymer conditioning of water treatment residuals

Conditioning of either wastewater biosolids or water treatment residuals conventionally utilizes a single polymer to improve subsequent dewatering. The sequential addition of two polymers has been reported to enhance biosolids dewaterability, but comparable benefits have not been demonstrated for water treatment residuals. This paper evaluated the use of cationic and nonionic polymers, singly and in combination (dual), to investigate whether dual polymer conditioning of residuals offers any advantages, and to determine whether the results could be accommodated by current mechanistic understandings. For this purpose, lab-scale tests used capillary suction time (CST), supernatant viscosity, zeta potential, streaming current, turbidity, floc size, and rheometric analyses. Comparisons of CST and viscosity results for single and dual polymer additions indicated that dual polymer use gave moderately improved dewaterability, possibly due to the increased mixing utilized for dual polymer addition. Using a cationic polymer produced a less turbid supernatant. Zeta potential and streaming current were not good indicators of conditioning efficacy when a nonionic polymer was used. Rheometric analyses were only meaningful in one selected method for treatment of the data: the area under the rheogram up to a shear rate of 30 inverse s. Overall, implementation of dual polymer use does not appear warranted

Physical characteristics of a waste activated sludge: conditioning responses and correlations with a synthetic surrogate

The efficient and economic management of waste activated sludge (WAS) requires a proper understanding of the sludge's material properties. Though there has been much study of WAS, an adequate linkage between its physical and chemical properties has been elusive. In particular, the conditioning and dewatering of WAS are expensive operations, and the addition of polymer to WAS leads to even more complex material behavior that is difficult to optimize. This paper reports on an extensive characterization of WAS, both with and without polymer conditioning. We combined the classical "jar test" approach with less conventional rheometric and electrokinetic measurements. In addition to the use of sampled WAS, a synthetic surrogate sludge was formulated, attempting to duplicate properties of WAS and allow more extensive characterization of a reproducible surrogate to WAS. Results with both the synthetic surrogate and WAS indicated that the traditional, electrokinetic, and rheological properties were related. However, the dose optima by rheometry were somewhat higher in both cases

Modem rheometric characterization of sludges

Historically, sludge was one of the first materials for which non-Newtonian behavior was recognized and quantified, due to the engineering challenge of properly pumping this material. Rheology is now employed in many fields, and over recent decades, more sophisticated rheometric techniques have been developed for a range of applications. This paper reviews some of these newer techniques and demonstrates their use in the characterization of sludge. The conventional technique of controlled shear rate (CSR) is used on a waste activated sludge with and without chemical conditioning. The "stress overshoot" phenomenon is observed and discussed, as it complicates the conventional interpretation of such test results. Newer methods are also applied for comparison: a creep test, which uses a constant applied stress while deformation is measured over time, and a strain amplitude sweep test. Neither of these methods experienced the type of difficulties seen with the CSR test. The creep test provides the critical stress level and, with sufficient data, the four parameters defining the Burgers model of deformation. The strain amplitude test provides the yield stress without model assumptions or reliance on data beyond the yield point

Use of drainability and filterability simulations for evaluation of oxidative treatment and polymer conditioning of sludge

In the traditional view of sludge structure, a two-phase system is visualized. The solid phase is often illustrated as consisting of uniform, spherical, negatively charged particles. This simplistic picture limits the understanding of both conditioning and dewatering. Specifically, it limits us to only two strategies for destabilization: charge neutralization (using cationic coagulant species with either uniform or patch effects), and bridging (using polymeric flocculants). In fact, the situation is more complex in many respects. In this paper, we compared chemical conditioning of anaerobically digested biosolids using (1) conventional polymeric flocculation, and (2) treatment by chemical oxidants. Since these strategies may alter dewatering behavior by very different mechanisms, we report comparisons using a lab-scale simulator of belt press dewatering, including separate steps for the drainage and filtration processes. This allows greater insight into the effects of these conditioning methods and how they might be properly employed

Quantification of hydrolytic charge loss of DMAEA-Q-based polyelectrolytes by proton NMR spectroscopy and implications for colloid titration

Copolymers of acrylamide and quaternised dimethylaminoethyl acrylate (DMAEA-Q) constitute an economically important range of cationic polyelectrolytes used in sludge conditioning. The latter treatment involves charge neutralisation and bridging induced by these polymers. Since both of these phenomena rely on charge-driven sorption onto the negatively charged colloidal particles, the accurate assessment of their charge density is of primary importance in polyelectrolyte characterisation. The experimental determination of this characteristic generally relies on colloidal charge titration, in which the cationic polymer is titrated against an anionic polymer. Hereby, one of the requirements to have a stoichiometric reaction between the oppositely charged polymers is a sufficiently low polymer concentration. In this study, it is shown that such a low polymer concentration may entail a pronounced hydrolysis effect for DMAEA-Q-based polymers, which leads to a release of the cationic side groups and hence causes considerable errors on the charge titration results. Proton nuclear magnetic resonance spectroscopy was applied to investigate the fast hydrolysis kinetics of DMAEA-Q polymers together with time-dependent charge titration measurements. Diffusion NMR spectroscopy was used to assist in establishing the nature of the hydrolysis compounds. The results from both techniques indicate that a high degree of hydrolysis is reached within minutes after dilution of a concentrated polymer stock solution into aqueous solutions of slightly acidic to neutral pH values. Therefore, a modification to the classic colloid titration procedure is proposed, using a buffered dilution liquid to avoid polymer hydrolysis. It is shown that a buffer pH value of 4.5 avoids not only polymer hydrolysis effects but also possible protonation of the anionic titrant, thereby avoiding overestimation of the charge density. By means of this procedure, reproducible and time-independent charge titration results are obtained