Effects of Ca 2+ on biological nitrogen removal in reverse osmosis concentrate and adsorption treatment

Artificial intelligence models for predicting calcium and magnesium removal by polyfunctional ketone using ensemble machine learners

Calcium (Ca2+) and magnesium (Mg2+) are the major scaling ions of reverse osmosis concentrate in zero-liquid discharge systems, causing performance decline. In this study, we predicted the removal of Ca2+ and Mg2+ from simulated reverse osmosis concentrate by functional polyketones (FPKs). Four amines, including 1,2-diaminopropane (DAP), 1-(2-aminoethyl) piperazine (AEP), 1-(3-aminopropyl) imidazole (API), and butyl amine (BA) used to synthesize FPKs. The effects of various factors such as the amount of adsorbent, feed water concentration, and pH were investigated for process optimization. In this study, ensemble learner artificial intelligence models, decision tree (DT), extreme gradient boost (XGB), and random forest (RF) were used to predict Ca2+ and Mg2+ removal by the FPKs. Datasets were collected experimentally using FPKs to remove Ca2+ and Mg2+ from the simulated reverse osmosis concentrate. The predictions were made by XGB, DT, and RF models for the first chosen amine for Ca2+ and then for Mg2+, subsequently, this process was repeated with each amine. The developed DT, RF, and XGB models demonstrated higher coefficients of determination for predicting Mg2+ removal by AEP and DAP (R2 = 0.841-0.935) than by API and BA (R2 = 0.774-0.801) except in the RF and XGB model results (R2 = 0.801-0.846). Overall, the XGB model displayed good results for both Ca2+ and Mg2+ removal but slight changes were observed in the AEP and BA predictions by DT and RF. Therefore, artificial intelligence models may be a viable alternative for further insight in predicting Ca2+ and Mg2+ removal by FPKs from simulated reverse osmosis concentrate.

Treating reverse osmosis concentrate to address scaling and fouling problems in zero-liquid discharge systems: A scientometric review of global trends

Currently, reverse osmosis concentrate (ROC) treatment is one of the most promising techniques for its disposal because it produces freshwater with high recovery and valuable materials such as salts and reduces waste volume and environmental pollution. Public attention to the severe consequences of water pollution and strict environmental regulations on wastewater discharge has pushed water-polluting industries toward zero-liquid discharge (ZLD). However, scaling and fouling problems increase energy consumption and limit permeate flux at high salt concentrations, mainly due to calcium, magnesium, and silica precipitation, ultimately decreasing ZLD performance. Therefore, this study discusses drivers and ROC pretreatment technologies to improve ZLD efficiency and presents a scientometric review of global trends. The advantages, disadvantages, and economic and environmental aspects of conventional and emerging pre-treatment technologies were studied. Traditional treatment of chemical processes combined with precipitation removes a large amount of scaling ions; however, high operation and maintenance costs and limited full-scale plant experience are the main drawbacks. Softening and coagulation are most commonly applied to treat large volumes at a moderate cost; however, substantial sludge production and increased conductivity are major operational issues. Moreover, emerging technologies efficiently remove scale-forming ions with high capital and operating costs. New variations in standard reverse osmosis technologies have improved ZLD efficiency; nonetheless, scaling and fouling are of concern. Therefore, this review presents the studies on ROC pre-treatment technologies for removing scaling ions to enhance ZLD efficiency, which can help in future research.

Hypothermia Pseudomonas taiwanensis J488 exhibited strong tolerance capacity to high dosages of divalent metal ions during nitrogen removal process

The nitrogen metabolic pathways of Pseudomonas taiwanensis J488 have not been confirmed from genomic function analysis and its divalent metal ion resistance remains poorly understood. In this study, the key denitrifying gene of Pseudomonas taiwanensis J488, nirB, was determined by draft genome sequencing. The nitrification of ammonium was insensitive to high concentrations of Ca(II), Mn(II), Zn(II), and Cd(II). Similarly, complete nitrite removal was achieved despite Mn(II) and Zn(II) reaching concentrations up to 30 mg/L. Furthermore, the efficiency of nitrate removal was significantly enhanced by 1.33%, 3.33%, 5.99%, and 1.53% with the addition of 0.5 mg/L Ca(II), 20 mg/L Mn(II), 5 mg/L Zn(II), and 2 mg/L Cd(II), respectively, comparison with the control. The bacterial growth in both nitrifying and denitrifying processes was substantially promoted by various dosages of divalent metal ions. These results indicate that divalent metal ions would not severely limit the capacity of strain J488 to purify nitrogen-polluted wastewater.

Effects of Ca2+ Concentration on Anaerobic Ammonium Oxidation Reactor Microbial Community Structure

The anaerobic ammonium oxidation (anammox) reaction removes nitrogen from wastewater, the performance of which is influenced by Ca2+; however, the effect of Ca2+ on microbial community structure is unclear. Therefore, the effects of Ca2+ concentration on the treatment performance of an anammox reactor and microbial community structure of anammox sludge were investigated. Ca2+ concentration minimally influenced the removal efficiency of NO2−–N and NH4+–N, but substantially influenced total N removal. Changing the Ca2+ concentration (between 25 and 125 mg/L) caused the average removal rate of total nitrogen to fluctuate by 3.3 percentage points. There were five major bacterial phyla in the anammox sludge: Proteobacteria, Chloroflexi, Acidobacteria, Planctomycete, and Chlorobi. Microbiological analysis revealed that the genera Acidobacterium, Anaerolinea, and Denitratisoma were positively correlated with Ca2+ concentration, and improved treatment performance of the anammox reactor. Moreover, uncultured Chlorobi bacterium clone RUGL1-218 (GQ421108.1) and uncultured sludge bacterium A21b (KT182572.1) may be key microorganisms for the immobilization of anammox bacteria. These findings offer a theoretical basis for improved wastewater treatment using the anammox process.

Ca(II) and Mg(II) significantly enhanced the nitrogen removal capacity of Arthrobacter arilaitensis relative to Zn(II) and Ni(II)

This study investigated the impacts of alkaline-earth metals [Ca(II), Mg(II)] and heavy metals [Zn(II), Ni(II)] on the nitrogen removal capacity of Arthrobacter arilaitensis Y-10. StrainY-10 was able to tolerate 20 mg/L Ca(II) and its ammonium removal efficiency was 100%. 0.5 mg/L Ca(II) effectively promoted total nitrogen removal from wastewater containing nitrite. Mg(II) supplementation substantially enhanced the bacterial growth and nitrogen reduction. As Mg(II) concentrations increased from 0 to 2 mg/L, the ammonium, nitrate and nitrite removal efficiencies increased by 40.62%, 69.91% and 64.68%, respectively. Although the nitrogen removal ability of strain Y-10 was sharply hindered by Zn(II) and Ni(II), it occurred continuously even when the Zn(II) concentration reached 30 mg/L. However, the ammonium and total nitrogen removal almost stopped at 8 mg/L Ni(II), and the denitrification capacity was lost when the Ni(II) concentration exceeded 1 mg/L. The results demonstrate that Ca(II) and especially Mg(II) could significantly enhance the nitrogen removal capacity of Arthrobacter arilaitensis relative to Zn(II) and Ni(II).

Coal chemical reverse osmosis concentrate treatment by membrane-aerated biofilm reactor system

Coal chemical reverse osmosis concentrate (ROC), which is characterized by high salinity and high organics, remains as a serious environmental problem. In this study, a lab-scale three-stage membrane-aerated biofilm reactor (MABR) system was designed to treat such a ROC. The effects of influent salinity and operating parameters (pH, DO and HRT) on the treatment efficiency were discussed. The removal efficiencies of COD, NH₄-N and TN under the optimal operating parameters reached to 81.01%, 92.31% and 70.72%, respectively. Simultaneous nitrification and denitrification (SND) as well as shortcut nitrogen removal were achieved. The salinity less than 3% did not induce significant decrease in treatment efficiency and microbial communities. Moreover, the dominant phyla in biofilms were Proteobacteria and Bacteroidetes. This work demonstrated MABR had great potential in ROC treatment.