Modelling of pH changes in alkaline lakes with water transfer from a neutral river

Impact of seasonal variations and water quality parameters on the formation of trihalomethanes and haloacetic acids in drinking water treatment processes

In this study, the combined effects of seasonal variations and water treatment processes on the formation of disinfection by-products (DBPs), focusing on trihalomethanes (THMs) and haloacetic acids (HAAs) within a full-scale conventional drinking water treatment plant, were investigated. The seasonal analysis revealed that autumn exhibited the highest levels of disinfection by-product formation potential (DBPFP), with trihalomethane formation potential (THMFP) and halo acetic acid formation potential (HAAFP) reaching 255 μg/L and 241 μg/L, respectively, likely due to increased organic matter from leaf fall and runoff. In contrast, winter exhibited the lowest concentrations, with THMFP at 150 μg/L and HAAFP at 56 μg/L. It is attributed to lower temperatures that limit organic matter reactivity. Correlations between 24 water quality parameters and DBPFP types were also examined, identifying critical parameters with the highest correlations. These parameters, including UV254 absorbance and total organic carbon, were used to develop regression models sensitive to seasonal changes and treatment stages. Among the treatment units, the coagulation and aeration stages achieved notable reductions in THM precursors, whereas HAA precursors were less effectively removed, persisting into secondary treatment stages. Chloroform was the predominant THM species, with a peak concentration of 100 μg/L in autumn, decreasing to 76 μg/L in summer, possibly due to increased volatilization in warmer months. For HAAs, dichloroacetic acid displayed the highest seasonal variability, peaking in autumn at 28 μg/L. These findings highlight the need for seasonally adaptive treatment strategies, particularly during high-risk autumn periods when DBPFP levels are elevated. This study provides actionable insights into optimizing treatment protocols to improve DBP control, emphasizing seasonal adjustments' critical role in ensuring compliance with water quality standards.

Influences of lower pH on phytoplankton growth in alkaline lakes after water transfer: Insights from a coupled hydrodynamic-algal ecological model and experimental analysis

Alkaline lakes with high pH and unique ecological communities often face water-level drawdown and ecological degradation problems due to climatic and hydrologic factors. Water transfer is becoming a popular method for solving these problems. However, a high pH is often considered the key to maintaining the stability of alkaliphilic algal communities, and a lower pH induced by water transfer from a neutral-pH river may threaten ecosystems in alkaline lakes. To explore the response characteristics of phytoplankton in alkaline lakes to pH changes, we conducted cultivation experiments on one species of dominant Cyanobacteria and one species of dominant Chlorophyta from alkaline lakes under different pH conditions. Subsequently, we constructed a coupled hydrodynamic and algal mathematical model considering the effect of pH to predict the dynamic changes in phytoplankton in a typical alkaline lake under water-transfer conditions. Both species are basophilic, and pH has a "low-inhibition and high-promotion" effect on their growth. A lower pH is detrimental to cyanobacterial growth and competitiveness, which may cause Cyanobacteria to lose their dominance in weakly alkaline environments with a pH < 8.5; additionally, water transfer causes a decrease in the total biomass and proportion of Cyanobacteria in Lake Chenghai, with decreases induced by pH changes accounting for 13.4% and 70.1%, respectively. The decrease in pH is the main reason for the decrease in dominance of Cyanobacteria after water transfer. These results provide a basic summary of the effects of pH changes on the algal growth in alkaline lakes and are a useful for formulating ecological water-transfer strategies for alkaline lakes.

Evaluation of a granular Cu-modified chitosan biocomposite for sustainable sulfate removal from aqueous media: A batch and fixed-bed column study

Adsorption-based treatment of sulfate contaminated water sources present challenges due to its favourable hydration characteristics. Herein, a copper-modified granular chitosan-based biocomposite (CHP-Cu) was prepared and characterized for its sulfate adsorption properties at neutral pH via batch equilibrium and fixed-bed column studies. The CHP-Cu adsorbent was characterized by complementary methods: spectroscopy (IR, Raman, X-ray photoelectron), thermal gravimetry analysis (TGA) and pH-based surface charge analysis. Sulfate adsorption at pH 7.2 with CHP-Cu follows the Sips isotherm model with a maximum adsorption capacity (407 mg/g) that exceeds most reported values of granular biosorbents at similar conditions. For the dynamic adsorption study, initial sulfate concentration, bed height, and flow rate were influential parameters governing sulfate adsorption. The Thomas and Yoon-Nelson models yield a sulfate adsorption capacity (146 mg/g) for the fixed bed system at optimized conditions. CHP-Cu was regenerated over 5 cycles (33 % to 31 %) with negligible Cu-leaching. The adsorbent also displays excellent sulfate uptake properties, regenerability, and sustainable adsorbent properties for effective point-of-use sulfate remediation in aqueous media near neutral pH (7.2). This sulfate remediation strategy is proposed for other oxyanion systems relevant to contaminated environmental surface and groundwater resources.