Acid precipitation-hydrothermal synthesis of needle-like hydroxyapatite for protein adsorption from waste phosphogypsum.

In order to promote the high-value utilization of waste phosphogypsum (PG), hydroxyapatite was directly synthesized from PG by acid precipitation-hydrothermal method (PGHAP), which was used for the adsorption of bovine serum albumin (BSA) and lysozyme (LYS). The synthesized PGHAP was characterized by XRD, SEM, FTIR and BET, and the effects of various factors on protein adsorption capacity were studied. The results showed that PGHAP exhibits a clear needle-like morphology, high crystallinity, and an average size of about 200 nm. The pH had the greatest effect on the adsorption of protein, and the highest adsorption capacity was obtained at pH 4.0. In addition, the adsorption mechanism of protein on PGHAP was explored by adsorption kinetics and adsorption isotherm. The adsorption of protein on PGHAP conforms to the Intra-particle diffusion model kinetic model, the maximum adsorption capacity of protein on PGHAP can reach 31 mg/g, which is comparable to other adsorbents in this field. In addition, the adsorption behaviour of PGHAP on protein is more appropriately described by Langmuir isotherm model, which indicates that the binding site with uniform energy on the surface of PGHAP realizes the monolayer adsorption of protein. The main adsorption mechanisms are ion exchange, co-precipitation, complexation reaction and so on. Therefore, the needle-like PGHAP synthesized from waste PG is a protein adsorbent with industrial application potential.

Optimization of a compact on-site stormwater runoff treatment system: Process performance and reactor design.

Stormwater runoff has become a major anthropogenic urban pollution source that threatens water quality. In this study, coagulation-sedimentation, and ammonium ion exchange and regeneration (AIR) modules were coupled as a CAIR system to efficiently treat stormwater runoff. In the coagulation module, 99.3%, 91.7%, and 97.0% of turbidity, total phosphorus, and chemical oxygen demand could be removed at an optimized poly-aluminum ferric chloride dosage of 30 mg/L, and the continuous experiment confirmed that the full load mode was more suitable for its rapid start-up. In the AIR module, dynamic ammonium removal indicated that the breakthrough time decreased with the rising initial concentration and superficial velocity. The Modified Dose Response (MDR) model described the ammonium exchange behavior better than the Thomas and the Bohart-Adams models. Then, a design flow of the ion exchange reactor was constructed by correlating constants in the MDR model with engineering parameters, and the ion exchange reactor was designed for continuous operation of the CAIR system. The average concentrations of chemical oxygen demand, total phosphorus, ammonium nitrogen, and total nitrogen in the effluent of the CAIR system were 7.22 ± 2.26, 0.17 ± 0.05, 1.49 ± 0.01, and 1.62 ± 0.02 mg/L, respectively. The almost unchanged exchange capacity and physicochemical properties after the multicycle operation confirmed the durability of zeolite for ion exchange. Techno-economic analysis suggested that the CAIR system is practically promising for stormwater management with efficient pollutants removal, small footprint, and acceptable operating cost.

Enhanced nutrient removal from stormwater runoff by a compact on-site treatment system.

Efficient and space-saving technologies for on-site treatment of stormwater runoff are required to control water pollution in the urban surface. The intermittent nature of stormwater runoff and extremely limited land available greatly hindered the application of current wastewater treatment technologies, and thus synchronous removal of multiple contaminants (especially for nutrient) efficiently was failed by current processes. In this study, a new compact CFFA treatment system, consisting of coagulation, flocculation, filtration and ammonium ion exchange units, was constructed for on-site treatment of stormwater runoff based on batch test optimization and pilot-scale test verification. The coagulation process effectively aggregated particles and precipitated phosphorus by dosing Al2(SO4)3, while flocculation using anionic polyacrylamide further enlarged particle size for efficient micromesh filtration. The dynamic micromesh filtration obtained turbidity and phosphorus removal efficiencies comparable to 30 min gravity settling with greatly smaller footprint. Ion exchange by zeolite showed higher exchange capacity owing to lower initial ammonium nitrogen concentration in the stormwater runoff. The pilot-scale experiments with treatment capacity of 1 L/s showed that the CFFA treatment system achieved synchronous removal of particles (97.2%), nitrogen (79.7%), phosphorus (95.0%) and organic matters (83.3%) efficiently within short hydraulic retention time of 0.35 h, yielding effluent with chemical oxygen demand, suspended solids, total phosphorus and total nitrogen of 38.7, 7.80, 0.22 and 2.80 mg/L, respectively. The CFFA treatment system had the highest pollutant removal loads compared to reported runoff treatment processes in literatures, and was well suited to on-site treatment of stormwater runoff with high space utilization efficiency.

Emerging wastewater treatment strategy for efficient nitrogen removal and compact footprint by coupling mainstream nitrogen separation with chemical coagulation and biological aerated filter.

In this study, an ammonia nitrogen (NH4+-N) ion exchange (IE) and regeneration (AIR) was constructed, and the chemical enhanced primary treatment (CEPT), AIR and biological aerated filter (BAF) were coupled in series to construct a novel CEPT-AIR-BAF process for efficient pollutants removal. At total hydraulic retention time of 4.6 h, the pilot-scale CEPT-AIR-BAF system obtained effluent with chemical oxygen demand of 17.9 ± 6.0 mg/L, NH4+-N of 0.5 ± 0.3 mg/L, total nitrogen of 2.4 ± 1.0 mg/L and total phosphorus of 0.08 ± 0.05 mg/L. AIR module achieved outstanding NH4+-N IE performance with NaClO-NaCl regeneration, and long-term regeneration increased surface area and mesopore of zeolites. Faster-growing heterotrophic bacteria, such as Pseudomonas and Comamonas, were enriched in BAF. The CEPT-AIR-BAF system saved at least 60% of land occupation and upfront investment, and the treatment cost ($ 0.155/m3) should be further reduced by investigations on the regeneration of loaded zeolite.

Compact wastewater treatment process based on abiotic nitrogen management achieved high-rate and facile pollutants removal.

Chemically enhanced primary treatment (CEPT), ammonium ion exchange and regeneration (AIR) and membrane bioreactor (MBR) were coupled as CAIRM to treat domestic wastewater compactly and efficiently. CAIRM achieved efficient removal of chemical oxygen demand, ammonia nitrogen, total nitrogen (TN) and total phosphorus with total hydraulic retention time of 4.6 h, and obtained 2.3 ± 0.9 mg/L TN in the effluent. CEPT removed phosphate and impurities and prevented AIR from pollution. AIR maintained excellent nitrogen removal with a slight decrease in the exchange capacity of ion exchangers. MBR polished the effluent from AIR, and the larger particle size and better dewaterability of sludge mitigated the membrane fouling. Many heterotrophic genera, such as Rhodobacter and Defluviimonas, were enriched in the oligotrophic MBR. This study demonstrates the viability and stability of CAIRM in efficient wastewater treatment, which will address critical challenges in insufficient nitrogen removal and high land occupancy of current processes.