Calcium peroxide (CaO₂) has been proven to oxidize various organic pollutants when they exist as a single class of compounds. However, there is a lack of research on the potential of unactivated CaO₂ to treat mixed chlorinated organic pollutants in soils. This study examined the potential of CaO₂ in treating soils co-contaminated with p-dichlorobenzene (p-DCB) and p-chloromethane cresol (PCMC). The effects of CaO₂ dosage and treatment duration on the rate of degradation were investigated. Furthermore, the collateral effects of the treatment on treated soil characteristics were studied. The result showed that unactivated CaO₂ could oxidize mixed chlorinated organic compounds in wet soils. More than 69% of the pollutants in the wet soil were mineralized following 21 days of treatment with 3% (w/w) CaO₂. The hydroxyl radicals played a significant role in the degradation process among the other decomposition products of hydrogen peroxide. Following the oxidation process, the treated soil pH was increased due to the formation of calcium hydroxide. Soil organic matter, cation exchange capacity, soil organic carbon, total nitrogen, and certain soil enzyme activities of the treated soil were decreased. However, the collateral effects of the system on electrical conductivity, available phosphorus, and particle size distribution of the treated soil were not significant. Likewise, since no significant release of heavy metals was seen in the treated soil matrix, the likelihood of metal ions as co-pollutants after treatment was low. Therefore, CaO₂ can be a better alternative for treating industrial sites co-contaminated with chlorinated organic compounds.

We investigate the use of hydrated lime and calcite waste marble powder as remediation treatments of contaminated jarosite-rich sediments from Portman Bay (SE, Spain), one of the most contaminated points in the Mediterranean coast by mining-metallurgical activities. We tested two commercial hydrated limes with different Ca(OH)₂ percentages (28 and 60% for Lime-1 and Lime-2 respectively) and two different waste marble powder, WMP, from the marble industry (60 and 96% of calcite for WMP-1 and WMP-2 respectively). Mixture and column experiments and modelling of geochemical reactions using PHREEQC were performed. Lime caused the precipitation of hematite, gypsum and calcite, whereas WMP treatments formed iron carbonates and hematite. The fraction of amorphous phases was mainly composed of iron oxides, hydroxides and oxyhydroxides that was notably higher in the lime treatment in comparison to the WMP treatment. The reactive surface area showed a positive trend with the amorphous phase concentration. Results highlighted the effectiveness of lime treatments, where Lime-2 showed a complete elimination of jarosite. Column experiments revealed a clear reduction of heavy metal concentration in the lixiviate for the treated sediments compared to the original sediments. Particularly, Lime-2 showed the highest reduction in the peak concentration of Fe, Mn, Zn and Cd. The studied treatments limited the stabilisation of Cr and Ni, whereas contrarily As increases in the treated sediment. PHREEQC calculations showed that the most concentrated heavy metals (Zn and Mn) are stabilized mainly by precipitation whereas Cu, Pb and Cd by a combination of precipitation and sorption processes. This chemical environment leads to the precipitation of stable iron phases, which sorb and co-precipitate considerable amounts of potentially toxic elements. Lime is significantly more effective than WMP, although it is recommended that the pH value of the mixture should remain below 9 due to the amphoteric behaviour of heavy metals.

Application of bioash from biofuel combustion to soil supports nutrient recycling, but may have unwanted and detrimental ecotoxicological side-effects, as the ash is a complex mixture of compounds that could affect soil invertebrates directly or through changes in their food or habitat conditions. To examine this, we performed laboratory toxicity studies of the effects of wood-ash added to an agricultural soil and the organic horizon of a coniferous plantation soil with the detrivore soil collembolans Folsomia candida and Onychiurus yodai, the gamasid predaceous mite Hypoaspis aculeifer, and the enchytraeid worm Enchytraeus crypticus. We used ash concentrations spanning 0–75 g kg⁻¹ soil. As ash increases pH we compared bioash effects with effects of calcium hydroxide, Ca(OH)2, the main liming component of ash. Only high ash concentrations above 15 g kg⁻¹ agricultural soil or 17 t ha⁻¹ had significant effects on the collembolans. The wood ash neither affected H. aculeifer nor E. crypticus. The estimated osmolalities of Ca(OH)2 and the wood ash were similar at the LC50 concentration level. We conclude that short-term chronic effects of wood ash differ among different soil types, and osmotic stress is the likely cause of effects while high pH and heavy metals is of minor importance.

Further steps are needed to establish feasible alleviation strategies that are able to reduce the impacts of ocean acidification, whilst ensuring minimal biological side-effects in the process. Whilst there is a growing body of literature on the biological impacts of many other carbon dioxide reduction techniques, seemingly little is known about enhanced alkalinity. For this reason, we investigated the potential physiological impacts of using chemical sequestration as an alleviation strategy. In a controlled experiment, Carcinus maenas were acutely exposed to concentrations of Ca(OH)2 that would be required to reverse the decline in ocean surface pH and return it to pre-industrial levels. Acute exposure significantly affected all individuals’ acid–base balance resulting in slight respiratory alkalosis and hyperkalemia, which was strongest in mature females. Although the trigger for both of these responses is currently unclear, this study has shown that alkalinity addition does alter acid–base balance in this comparatively robust crustacean species.

Inactivation of pathogens present in animal manure prior to land application has justified the use of advanced technologies. However, some alternatives are expensive or not effective due to the organic material and suspended solids present in the effluent (e.g., ozone, UV light). The use of hydrated lime (calcium hydroxide, Ca(OH)₂) is an attractive wastewater treatment option due to the ability of lime to kill pathogens and to extract phosphorus from manure at an alkaline pH. The present study aimed to evaluate the soluble phosphorus removal and pathogen inactivation (Escherichia coli, Salmonella enterica serovar typhymurium and Porcine circovirus type 2), in the liquid fraction and in the solid generated after Ca(OH)₂ addition in swine wastewater, exposed for 3 and 24 h at different pH conditions: 9.0, 9.5, and 10.0. The results showed the efficiency of pH elevation with Ca(OH)₂ in the removal of soluble P at pH 9.0 and the total inactivation of E. coli, Salmonella, and P. circovirus type 2 at pH 10.0. The liquid fraction (reuse water) could be safely used for cleaning the swine production facilities, and the solid fraction (precipitated P) could be used as a secondary product and fertilizer.

Concrete is usually the preferred material for construction of structures in contact with water during their service life. Early age exposure to water is beneficial for curing of concrete structures. However, the pollution of water from freshly cast concrete in contact with water has not been investigated in detail. A significant increase in the alkalinity has recently been observed in a stream in contact with freshly installed concrete culverts. High alkalinity has caused distress to fresh water fish in the stream. A preliminary laboratory study was commenced to explore the effect of leaching of alkali into water from freshly placed concrete. Freshly cast concrete specimens were exposed to fresh water, covering a range of conditions observed in the field such as volume of concrete/volume of water, age of exposure and cement content. Analysis of the results indicated that early age contact with fresh concrete can lead to an increase in the pH levels of water up to 11, similar to the levels of pH observed in pore water inside freshly cast concrete. It was noted that until an age of 4 days from casting of concrete, the age of exposure does not significantly affect the changes in the peak pH levels of water. Continuous monitoring of water in contact with concrete also indicated that the pH levels diminish with time, which is attributed to the possible reaction of calcium hydroxide with atmospheric carbon. The paper will present the experimental study, the results, analysis and outcomes as well as planning of a more comprehensive study to observe possible ways of reducing the leaching of alkali from freshly placed concrete.

A fish canning facility processes 1900–2000 tons of mackerel and sardine annually at arate of 10–15 tons per day for a total of 200 days yr⁻¹. This factory generates an average of 20 m³ of industrial wastewaters per day. The objective of our study, which was carried out on a bimonthly basisfrom December 1995 to November 1996, was to determine the overall pollutant load associated with this effluent in relation to the applicable Egyptian Standards and to propose methods for pollutant load reduction before discharging it to the local sewer. The methods were to benefit through the recovery of wasted organic load and transform it into an environmentally safe residue amenable for either immediate reuse or final disposal thereafter. Five chemical coagulation/flocculation treatments were tried using ferric chloride, alum, lime, ferric chloride and lime, and alum and lime. The best method involved the use of FeCl₃ and Ca(OH)₂ (0.4 g Fe L⁻¹ and 0.2 g Ca L⁻¹, respectively) which reduced the average influent BOD₅ from 989 to 204 mg L⁻¹, the COD from 1324 to 320 mg L⁻¹, TSS from 4485 to 206 mg L⁻¹, total protein content from 812 to 66 mg L⁻¹ and oil and grease from 320 to 66 mg L⁻¹. The separated dried precipitate averaged 50 g L⁻¹ which was found to contain 40% by weight recovered protein and 20% recovered fat. The solid was ideal for on-site reprocessing as animal feed. As well, the final effluent, if not discharged to the area sewer, was safe for controlled use in some irrigation applications or forestry projects at the desert area surrounding the factory.

Solidification of cathode ray tube (CRT) panel glass was carried out using a hydrothermal processing method. In this way, the glass powder was first compacted in a mold at 20 MPa, and then hydrothermally cured in an autoclave under saturated steam pressure at 200 ℃ for 6 h. The CRT panel glass was then hydrothermally solidified by the formation of tobermorite (Ca₅Si₆O₁₆(OH)₂·4H₂O), which was encouraged by the addition of slaked lime (Ca(OH)₂). The strength of solidified specimen heavily depended on the amount of tobermorite formed, with higher concentrations of tobermorite producing commensurately greater mechanical strength. With the addition of Ca(OH)₂ at 20–30% by mass, the specimen achieved a bending strength of approximately 16 MPa, which was sufficiently great for using as a construction material. As such, there is cause to believe that the hydrothermal processing method used here may have great potential for resource utilization of CRT panel glass, and the performance of the product is suitable for use as building materials.

Reduction in the dissolved phosphorus (P) desorption from agricultural soils could be an effective measure to prevent eutrophication. Lime is a high calcium–containing mineral that can have promising but varying responses on P desorption depending on soil type. The main objective of this research was to evaluate and compare the potential of hydrated lime and lime kiln dust, its cheaper alternative, as soil amendments to increase soil P adsorption capacity and to reduce dissolved P desorption from four soil types (sandy, sandy loam, loam, and clay loam). A batch adsorption study with varying P concentrations of 0, 0.2, 0.4, 0.6. 0.8, and 1.0 mM P and an adsorbent dose of 1% lime by air-dried soil mass at a fixed pH of 6.5 was carried out. The adsorption data fit best the Freundlich adsorption isotherm model. Both hydrated lime and lime kiln dust significantly increased the Freundlich adsorption coefficient by 3.2, 2.4, 2.0, and 1.6 times in loam, sandy, sandy loam, and clay loam soils, respectively. Although the hydrated lime showed a higher potential to increase the Langmuir maximum adsorption capacity in comparison to lime kiln dust, they both exhibited similar performance at lower P concentration ranges that are representative of the soil solution. The cumulative phosphorus desorption in the ten consecutive days agreed with the adsorption results. Therefore, lime kiln dust as a by-product could be a promising soil amendment to increase soil phosphorus adsorption capacity leading to less phosphorus desorption to water bodies. Further studies on its interaction with crop growth at field scale are required.

Chemical phosphorus removal with hydrated lime was evaluated on effluents from different biological treatment processes applied to swine manure. The objective of this study was to establish the most suitable process for this kind of wastewater treatment. Effluents a UASB reactor, a nitrification reactor (NR), a modified Lutzak–Ettinger (MLE) reactor and a deammonification (DMX) reactor were evaluated. A comprehensive study was developed at laboratory scale to evaluate the effect of possible interferences, including alkalinity, total organic carbon, and ammonia, on phosphorus precipitation. The highest soluble phosphorus (Pₛₒₗ) removal efficiency and the lowest Ca:P molar ratio were obtained for the NR effluent (92% and 2.0, respectively). The good performance of the NR effluent could be attributed to the low level of ammoniacal nitrogen and alkalinity and to the presence of a relatively high concentration of calcium. Highly promising results were also obtained in field experiments, where a phosphorus removal unit was installed as the last step in a swine manure treatment system, and precipitation was applied to effluent from the NR. In this case, efficiencies of Pₛₒₗ removal higher than 90% were obtained. The produced sludge was rich in phosphorus and could be used as, for example, fertilizer. The results obtained in this work showed the importance of applying an efficient treatment system to swine manure for reduction of ammoniacal nitrogen, alkalinity, and carbon before chemical removal of phosphorus by precipitation with hydrated lime.