Effect of solution composition on seeded precipitation of calcium for high recovery RO of magnesium-bearing wastewater, surface water or groundwater

Pilot-scale study on seeded precipitation assisted nanofiltration for flue-gas desulfurization wastewater softening

In order to reduce the cost of chemical softening, the seeded precipitation assisted nanofiltration (NF) process was introduced into zero liquid discharge (ZLD) of flue-gas desulfurization (FGD) wastewater treatment. A pilot-scale system was developed and run for 168 h in a coal-fired power plant. The system mainly consists of lime softening, ambient temperature crystallizer (ATC) and NF, in which the raw water treatment capacity was 1 m³/h. The results indicated that the system operated stably, the softening cost was 13.30 RMB/m³, and the electricity cost was 3.39 RMB/m³ for the FGD wastewater in this pilot system. High quality gypsum was got from the ATC unit, of which the purity was 95.8%. Through this system, the hardness removal rate was higher than 98.9% and the water recovery rate reached 96%. In addition, the pressure and permeate flux kept stable in the ultrafiltration (UF) unit and NF unit, indicating no scaling occurred in the two units during 168 h test. Thus, a feasible and cost-effective process was provided by using the seeded precipitation assisted NF to deal with the FGD wastewater.

Phosphate removal from food industry wastewater by chemical precipitation treatment with biocalcium eggshell

The physicochemical treatment (PT) of food industry wastewater was investigated. In the first stage, calcium magnesium acetate (CaMgAc₄) was synthesized using eggshell (biocalcium), magnesium oxide and acetic acid in a 1:1:1 stoichiometric ratio. In the synthesis process, the thermodynamic parameters (ΔH, ΔS and ΔG) indicated that the reaction was endothermic and spontaneous. The samples were characterized by infrared spectroscopy (IR), scanning electronic microscopy (SEM), X-ray diffraction (XRD) and electron X-ray dispersive spectroscopy (EDS). CaMgAc₄ was used to precipitate the phosphate matter. IR analysis revealed that the main functional groups were representative of the acetate compounds and the presence of OH^- groups and carbonates. In the physicochemical treatment, a response surface design was used to determine the variables that influence the process (pH, t, and concentration), and the response variable was phosphorus removal. The treatments were carried out in the wastewater industry with an initial concentration of 658 mg/L TP. The optimal conditions of the precipitation treatment were pH 12, time 12 min, and a CaMgAc₄ concentration of 13.18 mg/L. These conditions allowed the total elimination (100%) of total phosphorus and phosphates, 81.43% BOD₅ and 81.0% COD, 98.9% turbidity, 95.01% color, and 92% nitrogen matter.

Desupersaturation of RO concentrate and gypsum removal via seeded precipitation in a fluidized bed crystallizer

The feasibility of a continuous chemically-enhanced seeded precipitation (CCESP) process was evaluated for desupersaturation of primary reverse osmosis (PRO) concentrate generated from RO desalting of inland agricultural drainage (AD) water with high gypsum scaling potential. The CCESP approach, comprised of partial lime treatment (PLT) followed by gypsum seeded precipitation (GSP), was assessed via laboratory and field tests, along with model simulations. PLT effectiveness was confirmed for residual antiscalant removal from the PRO concentrate, which otherwise would suppress gypsum crystallization. GSP was carried out in a fluidized bed crystallizer (FBC) demonstrating the feasibility of continuous PRO concentrate desupersaturation with suitable solids management. FBC operation was stable, with respect to desupersaturation performance, when operating over a sequence of periodic solids purge-only mode with intermittent seeds replenishment. The study suggests that CCESP integration with primary and secondary RO desalting (i.e., PRO-CCESP-SRO) can provide for significant enhancement of product water recovery for inland water of high gypsum scaling propensity. For example, source water of high salinity (14,347 mg/L total dissolved solid) AD water, nearly saturated with respect to gypsum, could be desalted up to a recovery of 88-96% (relative to merely 66% recovery feasible via PRO desalting. Moreover, net salt harvesting of 2.6-3.6 kg per m³ RO concentrate (with concentrate recycle) can be obtained from high recovery desalting of the above PRO concentrate.

Investigation of Lithium Application and Effect of Organic Matter on Soil Health

The extensive use of lithium (Li) ion-based batteries has increased the contamination of soil and water systems due to widespread dispersal of Li products in the environment. In the current study, the influence of Li application on soil fertility and leachate was observed. Three soil samples were collected and five treatments of Li (0, 50, 100, 150 and 200 mg/L) were applied. After three months of Li treatment, leachate was collected and soil samples were subjected to physical and chemical analyses. The results showed that the mean values of soil pH were increased slightly after Li application while electrical conductivity (EC) ranged from 1.2 to 5.1 µS/cm, indicating that soil was slightly saline in nature. The sodium was observed to be greater than the recommended values (0.3–0.7 mg/kg) in Li-amended soil while calcium and magnesium values decreased in soils compared to untreated soil. Mean values of phosphorus and potassium were greater before Li application and reduced considerably after Li application. Leachate analysis showed that all the parameters differed significantly except those of zinc and iron. The EC of leachate samples ranged from 2286–7188 µS/cm, which shows strong salinity. The sodium adsorption ratio (SAR) ranged from 1–11, which indicates that it falls into the marginal soil category. Lithium concentration in leachate samples ranged from 0–95 mg/L, which was significantly higher than the acceptable value for lithium (2.5 mg/L) in leachate. A soil sample (3) with an additional 10% organic matter showed that after Li application, the loss of nutrients in leachate was less as compared to the other two samples, demonstrating that organic matter improved soil conditions and suppressed the negative effects of Li on soil. Our results could raise concerns about risks in situations where food and fodder crops are associated with Li-contaminated waste disposal.

Integration of two-stage nanofiltration with arsenic and calcium intermediate chemical precipitation for gold mining effluent treatment

The aim of this study was to evaluate an innovative treatment route for gold-mining effluents rich in calcium, arsenic, and sulfate. This treatment route comprised two nanofiltration (NF) stages and a two-step intermediate precipitation. Arsenic and iron coprecipitation (first step) and calcium carbonate precipitation (second step) were assessed aiming to treat the first-stage NF concentrate and increase the permeate recovery rate in a second-stage NF. The pH, the molar ratio of Fe/As (first step), and the molar ratio of CO₃/Ca (second step) were optimized by using rotational central composite design. Under optimal conditions, the arsenic removal was 99.8% (at pH = 7.0 and Fe/As = 4.0), and the calcium removal was 99.5% (at pH 11.5 and CO₃/Ca = 3.5). The supernatant of Ca precipitation had very basic pH and had to be acidified before the second-stage NF. The pH 8.5 proved to be the best one regarding retention efficiency and flux. The flux decay of the second-stage NF was attributed to both osmotic pressure increase and reversible fouling resistance. It was concluded that the proposed treatment system is efficient for the treatment of gold-mining wastewater, ensuring higher production of treated effluent and an easy disposable of the final concentrate.