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Phosphorus recovery from sewage sludge ash through an electrodialytic process

The electrodialytic separation process (ED) was applied to sewage sludge ash (SSA) aiming at phosphorus (P) recovery. As the SSA may have high heavy metals contents, their removal was also assessed. Two SSA were sampled, one immediately after incineration (SA) and the other from an open deposit (SB). Both samples were ED treated as stirred suspensions in sulphuric acid for 3, 7 and 14 days. After 14 days, phosphorus was mainly mobilized towards the anode end (approx. 60% in the SA and 70% in the SB), whereas heavy metals mainly electromigrated towards the cathode end. The anolyte presented a composition of 98% of P, mainly as orthophosphate, and 2% of heavy metals. The highest heavy metal removal was achieved for Cu (ca. 80%) and the lowest for Pb and Fe (between 4% and 6%). The ED showed to be a viable method for phosphorus recovery from SSA, as it promotes the separation of P from the heavy metals.

Electrokinetic remediation of six emerging organic contaminants from soil

Some organic contaminants can accumulate in organisms and cause irreversible damages in biological systems through direct or indirect toxic effects. In this study the feasibility of the electrokinetic (EK) process for the remediation of 17β-oestradiol (E2), 17α-ethinyloestradiol (EE2), bisphenol A (BPA), nonylphenol (NP), octylphenol (OP) and triclosan (TCS) in soils was studied in a stationary laboratory cell. The experiments were conducted using a silty loam soil (S2) at 0, 10 and 20mA and a sandy soil (S3) at 0 and 10 mA. A pH control in the anolyte reservoir (pH>13) at 10 mA was carried out using S2, too. Photo and electrodegradation experiments were also fulfilled. Results showed that EK is a viable method for the remediation of these contaminants, both through mobilization by electroosmotic flow (EOF) and electrodegradation. As EOF is very sensible to soil pH, the control in the anolyte increased EOF rate, consequently enhancing contaminants mobilization towards the cathode end. The extent of the mobilization towards the electrode end was mainly dependent on compounds solubility and octanol-water partition coefficient. In the last 24h of experiments, BPA presented the highest mobilization rate (ca. 4 μg min(-1)) with NP not being detected in the catholyte. At the end of all experiments the percentage of contaminants that remained in the soil ranged between 17 and 50 for S2, and between 27 and 48 for S3, with no statistical differences between treatments. The mass balance performed showed that the amount of contaminant not detected in the cell is similar to the quantity that potentially may suffer photo and electrodegradation.

Valorisation of ferric sewage sludge ashes: potential as a phosphorus source

Sewage sludge ashes (SSA), although a waste, contain elements with socio-economic and environmental potential that can be recovered. This is the case of phosphorus (P). SSA from two Danish incinerators were collected during two years and characterized. The sampling was done immediately after incineration (fresh SSA) or from an outdoor deposit (deposited SSA). Although morphology and mineral composition were similar, physico-chemical and metal concentration differences were found between incinerator plants and sampling periods. No differences were observed between deposited and fresh SSA, except for the parameters directly influenced by disposal conditions (e.g. moisture content). All the SSAs had high concentrations of P (up to 16wt%), but they all exceeded Danish EPA Cd and Ni thresholds for direct application at agricultural soil. Fresh and deposited SSA were acid washed aiming P extraction, achieving 50gP/kg (approx. 37% of total P), but metals were also co-extracted to the liquid phase. To avoid and/or minimize the metals pollution of the extracted P, selective P recovery from the SSA was tested, using the electrodialytic (ED) process. ED laboratory cells, with 3 compartments (3c) and 2 compartments (2c), and two acid concentrations (H2SO4, 0.08M and 0.19M) were used for 7days. The most concentrated acid solution increased P solubilization. The 2c-cell combined with the higher acid concentration resulted in higher P recoveries, 125g of P/kg of SSA in the anolyte. The obtained results showed that the ED process is a valuable tool for the SSA valorisation as it promotes simultaneous P recovery and metals extraction from the SSA.

Removal of Pharmaceutical and Personal Care Products in Aquatic Plant-Based Systems

The use of pharmaceuticals and personal care products (PPCPs) is growing as they are used not only for treatment but also for prevention of illnesses. In wastewater treatment plants (WWTPs) many PPCPs are not completely degraded/removed, which contributes for their frequent detection in, e.g. salt marsh areas. These areas may be considered a sink, source and cycling centre of contaminants on the receiving water body flow rate. In this chapter, a study about the potential of salt marsh plants Halimione portulacoides and/or Spartina maritima for the removal of three PPCPs, caffeine (CAFF), oxybenzone (HMB) and triclosan (TCS), is summarized. Experiments, at microcosms level, had two main aims: (1) the simulation of natural estuarine environment and study of dispersion mechanisms and “natural” remediation potential of target PPCPs and (2) the optimization of biological treatment technologies in WWTPs by simulating constructed wetland composed by plants and light expanded clay aggregates (LECA). Results indicate that either in estuaries or in WWTP the presence of a physical support can help to decrease contaminant levels mainly through sorption processes. The tested salt marsh species also showed potential to directly or indirectly promote the remediation of contaminants. In any case the remediation potential and dispersion mechanism are highly dependent from the characteristics of contaminants, like octanol–water partition coefficient (Log Kow) and solubility.

Electrodialytic 2-compartment cells for emerging organic contaminants removal from effluent

The present work discusses the efficiency of the electrodialytic (ED) process to remove emerging organic contaminants (EOCs) from effluent. The ED process was carried out in a cell of two-compartments (2 C-cell) with effluent in either the anode or cathode compartment, separated from the electrolyte compartment through an anion or a cation exchange membrane (AEM and CEM, respectively). As effluent destination might be soil irrigation, and having in mind the nutrient recycling, phosphorus was also monitored in the process. The ED removals showed to be dependent of EOCs characteristics and cell design. Removals were higher when using an AEM (60-72%) than a CEM (8-63%), except for caffeine when the effluent was placed in the cathode, that did not show any removal. When using an AEM with the effluent placed in the anode compartment, all the EOCs (including caffeine) were removed between 57-72%, mainly through electrodegradation phenomena. Regarding phosphorus, a polarity switch may be done to a 2 C-cell with a AEM, depending on the effluent final use. This technology is still in its first steps and, in both cases, further optimization of ED parameters is needed. Still, this technological innovation and cross-cutting research envisages the promotion of economic, social and environmental benefits.

Remediation of Pharmaceutical and Personal Care Products (PPCPs) in Constructed Wetlands: Applicability and New Perspectives

Nowadays, wastewater treatment plants (WWTPs) considered not very effective in removing all types of organic compounds, including pharmaceuticals and personal care products (PPCPs). The effluent discharged containing PPCPs shows negative impact on fresh/marine waters, even at vestigial concentrations. The integration of constructed wetlands (CWs) as a biological treatment technology in WWTPs may be an option to effective removal of PPCPs, which is crucial for water bodies’ protection. On the other hand, if they arrive to water bodies it is important to understand the self-restoration capacity of the system. This chapter makes an overview (based on literature and experimental data) about the effectiveness of CWs as a polishing step in WWTPs and the potential to remove contaminants if they arrive to salt marsh areas. In both cases, there is a same principle behind. CWs defined as artificially engineered ecosystems designed and constructed to control biological processes as in natural wetlands, but in a controlled natural environment.

Phytoremediation Coupled to Electrochemical Process for Arsenic Removal from Soil

Amongst environmental contamination problems, soil contamination with metals and metalloids may represent a big threat due to the high toxicity and widespread presence of mining activities. Electrokinetic (EK) process relies on the application of a low level direct current between electrodes in a partially saturated or even saturated soil and appears as a promising in situ strategy for fine-grained contaminated soils. Due to its mobilization potential, EK process can be considered as an integrated tool for contaminants removal, alone and coupled with phytoremediation. The coupling of EK process with phytoremediation (also known as EK-assisted phytoremediation) is an innovative technique that deserves a deeper knowledge to enlarge the scope of EK application. The EK-enhanced phytoremediation aims to use the presence of plants to counteract the effects of the electric current as it brings most of the benefits of a “regular” phytoremediation scheme (e.g., recovery of soil properties and improvement of its structure).

Phytoremediation and the Electrokinetic Process: Potential Use for the Phytoremediation of Antimony and Arsenic

Remediation of soils contaminated with metals and/or metalloids is of special importance due to the increasing number of mining activities or, on the other hand, to their closing which will produce environmental residues.