Co-conditioning of the anaerobic digested sludge of a municipal wastewater treatment plant with alum sludge: benefit of phosphorus reduction in reject water

Application of Alum Sludge in Wastewater Treatment Processes: “Science” of Reuse and Reclamation Pathways

Alum sludge (AlS) refers to the inevitable by-product generated during the drinking water purification process, where Al-salt is used as a coagulant in the water industry. It has long been treated as “waste”, while landfill is its major final disposal destination. In fact, AlS is an underutilized material with huge potential for beneficial reuse as a raw material in various wastewater treatment processes. In the last two decades, intensive studies have been conducted worldwide to explore the “science” and practical application of AlS. This paper focuses on the recent developments in the use of AlS that show its strong potential for reuse in wastewater treatment processes. In particular, the review covers the key “science” of the nature and mechanisms of AlS, revealing why AlS has the potential to be a value-added material. In addition, the future focus of research towards the widespread application of AlS as a raw material/product in commercial markets is suggested, which expands the scope for AlS research and development.

Integrating alum sludge with waste-activated sludge in co-conditioning and dewatering: a case study of a city in south France

The unique geographical location of waterworks and wastewater treatment plant (WWTP) in Graulhet (France) profited the environmental resource integration and "Circular Economy." Alum sludge from a local waterworks was introduced to co-conditioning and dewatering with waste-activated sludge from a nearby WWTP to examine the role of the alum sludge in improving the dewaterability of the mixed sludge. Experiments demonstrated that the optimal mixing ratio was 1:1 (waste-activated sludge/alum sludge, v/v). Alum sludge has been shown to beneficially enhance mixed sludge dewaterability, by decreasing both the specific resistance to filtration (SRF) and the capillary suction time (CST). Moreover, the optimal polymer (Sueprfloc-492HMW) dose for the mixed sludge (mix ratio 1:1) was 200 mg/L, highlighting a huge savings (14 times) in polymer addition without alum sludge involvement. In addition, cost-effective analysis of its potential full-scale application has demonstrated that the initial investment could be returned in 11 years. The co-conditioning and dewatering strategy can be viewed as a "win-win" strategy for the Graulhet, France, water and wastewater industry. Graphical abstract.

How can sludge dewatering devices be assessed? Development of a new DSS and its application to real case studies

A key issue in biological Waste Water Treatment Plants (WWTPs) operation is represented by the sludge management. Mechanical dewatering is a crucial stage for sludge volume reduction; though, being a costly operation, its optimization is required. We developed an original experimental methodology to evaluate the technical (dewatering efficiency) and financial (total treatment costs) performance of dewatering devices, which might be used as a DSS (Decision Support System) for WWTP managers. This tool was then applied to two real case studies for comparing, respectively, three industrial size centrifuges, and two different operation modes of the same machine (fixed installation vs. outsourcing service). In both the cases, the best option was identified, based jointly on economic and (site-specific) technical evaluations.

Drinking water treatment residuals: a review of recent uses

Coagulants such as alum [Al2(SO4)3 x 14H2O], FeCl3, or Fe2(SO4)3 are commonly used to remove particulate and dissolved constituents from water supplies in the production of drinking water. The resulting waste product, called water-treatment residuals (WTR), contains precipitated Al and Fe oxyhydroxides, resulting in a strong affinity for anionic species. Recent research has focused on using WTR as cost-effective materials to reduce soluble phosphorus (P) in soils, runoff, and land-applied organic wastes (manures and biosolids). Studies show P adsorption by WTR to be fast and nearly irreversible, suggesting long-term stable immobilization of WTR-bound P. Because excessive WTR application can induce P deficiency in crops, effective application rates and methods remain an area of intense research. Removal of other potential environmental contaminants [ClO4-, Se(+IV and +VI), As(+III and +V), and Hg] by WTR has been documented, suggesting potential use of WTR in environmental remediation. Although the creation of Al plant toxicity and enhanced Al leaching are concerns expressed by researchers, these effects are minimal at circumneutral soil pH conditions. Radioactivity, trace element levels, and enhanced Mn leaching have also been cited as potential problems in WTR usage as a soil supplement. However, these issues can be managed so as not to limit the beneficial use of WTR in controlling off-site P losses to sensitive water bodies or reducing soil-extractable P concentrations.

The cost and effectiveness of solids thickening technologies for treating backwash and recovering nutrients from intensive aquaculture systems

The cost and effectiveness of three solids thickening processes, i.e., gravity thickening settlers (GTS), inclined belt filters (IBF), geotextile bag filters (GBF), were individually evaluated with the biosolids backwash produced in intensive aquaculture systems equipped with microscreen drum filters and radial-flow settlers. The IBF produced the cleanest discharge and highest treatment efficiencies, likely reflecting the rapid efficiency with which solids are separated from wastewater. The GBF was the least effective process, i.e., GBF leachate contained the highest concentrations of TP, TN, and cBOD. However, GBF was most effective for sludge volume reduction. Capital cost estimates for an IBF were more than twice that of GTS and GBF of similar treatment capacity. The GTS had the lowest capital and annual operating cost estimates. The estimated annual operating cost of the GBF was orders of magnitude higher than the IBF and GTS, due to the high cost to replace bags.