The impact of ferrous ion reduction of chlorite ion on drinking water process performance

The use of chlorine dioxide (ClO₂) as a primary disinfectant and pre-oxidant in drinking water treatment is being explored as an alternative to chlorine for reducing disinfection by-product formation and to assure compliance with United States Environmental Protection Agency's Stage 1 Disinfection/Disinfection By-Products Rule. However, the ClO₂ by-product chlorite ion (ClO₂⁻) is also regulated by the same regulation. Ferrous iron (Fe(II)) has been shown to effectively reduce chlorite ion to chloride ion (Cl⁻) and this study was conducted to evaluate the impact on overall treatment process performance due to the ferric hydroxide solids that form from the reaction. Ferrous iron application was explored at three different points in a pilot-scale water treatment system: pre-rapid mix, pre-settling and pre-filter. Chlorite ion concentrations were effectively reduced from 2 mg/L to less than 0.3 mg/L using an Fe(II) dose of approximately 6 mg/L for all trials. Fe(II) addition at the rapid mix caused no adverse effects and, in fact, allowed for reduction of the alum dose due to the newly formed ferric hydroxide acting as a supplemental coagulant. An increase of 241 and 247% of total suspended solids influent to the filter process was observed when Fe(II) was applied at the pre-settling and pre-filter locations. Pilot-scale filter runs during these trials were less than 2 h and never obtained true steady state conditions. Jar testing was performed to better understand the nature of the ferric hydroxide solids that are formed when Fe(II) was oxidized to Fe(III) and to explore the effectiveness of Fe(II) addition at intermediate stages in the flocculation process.     

Effect of bromide ions on genotoxicity of halogenated by-products from chlorination of humic acid in water

Genotoxicity of halogenated by-products obtained by chlorination of humic acid in water was evaluated in the presence of bromide ions (Br⁻). After the halogenated humic acid solution was made to flow through CSP800 cartridge, absorbed substances were eluted with dimethyl sulfoxide or acetone, and subjected to mutagenicity assays and to analysis of trihalomethanes (THMs). Mutagenic activity was measured by Ames tests using S. typhimurium TA100 strain without metabolic activation, and by the frequencies of micronuclei formation using cultured Chinese hamster lung cells (CHL/IU) in vitro. A powerful effect of bromide ions in chlorinated humic acid solutions was observed on the reverse mutation and micronuclei formations. The formations of total THMs and more brominated THMs were also enhanced in the presence of bromide ions. The ratio of [Br⁻/Cl⁻] regulated the composition and concentrations of THMs intensely, and the rate of substitution of Br⁻ was greater than that of chloride ions (Cl⁻). The increments of the mutagenicity and total THMs formed in chlorinated solutions were observed in parallel with the concentration of Br⁻ or Cl⁻. From the observations, it was concluded that the increasing mutagenicity might be caused by the increasing chlorinated and/or brominated by-products.     

Development of an advanced biological treatment system applied to the removal of nitrogen and phosphorus using the sludge ceramics

To develop a method of forming lake sediment into sludge ceramics with porosity and good biological adhesion for use as a medium for microorganisms in wastewater treatment, a study of the effects of forming conditions was conducted by adjusting the water content of sludge and compounding some additives. By adjusting the water content of the raw material at the kneading/pelletizing step to 40–42% and adding 3% waste glass to the raw materials to make up for the lack of flux, a sludge ceramic with a density in terms of specific gravity of saturated surface dry aggregate of about 1400 kg m⁻³ was formed. In addition, to develop a small-scale wastewater treatment system capable of removing nitrogen and phosphorus, a sludge ceramic was applied as a medium for biological filtration. The results indicated that the BOD removal nitrification rate were superior to those of conventional ceramic media, reached at 95.3% and 87.4%, respectively. The introduction of iron electrolysis resulted in high treatment performance achieving BOD levels of 10 mg L⁻¹ or less, T-N of 10 mg L⁻¹ or less and T-P of 1 mg L⁻¹ or less.     

Application of machine learning technique for predicting and evaluating chloride ingress in concrete

The degradation of concrete structure in the marine environment is often related to chloride-induced corrosion of reinforcement steel. Therefore, the chloride concentration in concrete is a vital parameter for estimating the corrosion level of reinforcement steel. This research aims at predicting the chloride content in concrete using three hybrid models of gradient boosting (GB), artificial neural network (ANN), and random forest (RF) in combination with particle swarm optimization (PSO). The input variables for modeling include exposure condition, water/binder ratio (W/B), cement content, silica fume, time exposure, and depth of measurement. The results indicate that three models performed well with high accuracy of prediction (R²≥ 0.90). Among three hybrid models, the model using GB_PSO achieved the highest prediction accuracy (R² = 0.9551, RMSE = 0.0327, and MAE = 0.0181). Based on the results of sensitivity analysis using SHapley Additive exPlanation (SHAP) and partial dependence plots 1D (PDP-1D), it was found that the exposure condition and depth of measurement were the two most vital variables affecting the prediction of chloride content. When the number of different exposure conditions is larger than two, the exposure significantly impacted the chloride content of concrete because the chloride ion ingress is affected by both chemical and physical processes. This study provides an insight into the evaluation and prediction of the chloride content of concrete in the marine environment.     

玄武岩机制砂混凝土抗硫酸盐侵蚀性能

为了研究玄武岩机制砂混凝土抗硫酸盐侵蚀性能,采用了河砂（HS）、河砂+机制砂（HS+JZ）、机制砂（JZ）三个配比,设定了7.5%（质量分数）MgSO₄和15%（质量分数）MgSO₄两种溶液环境下进行干湿循环试验,通过测试质量损失率、超声波声速、相对动弹性模量和抗压强度比,结合内部裂缝与内部微观结构进行了分析。结果表明:18次干湿循环后在7.5%MgSO₄和15%MgSO₄两种溶液中3种混凝土的质量损失率分别增长到6.6%,5.5%,4.5%和8.9%,7.6%,6.5%;超声波声速值分别下降到3.600,3.684,3.800 km·s^-1和3.238,3.368,3.444 km·s^-1;相对动弹性模量分别降到64%,68%,76%和55%,57%,67%;抗压强度比分别降到0.84,0.83,0.88和0.72,0.75,0.78;河砂混凝土最终的侵蚀产物主要以白色纤维状结晶体钙矾石为主,玄武岩机制砂混凝土的侵蚀产物主要以白色石膏为主;玄武岩机制砂含少量石粉和自身的耐侵蚀性可有效提高混凝土抗硫酸盐侵蚀的能力。     

Removal of bisphenol A by a nanofiltration membrane in view of drinking water production

The efficiency with which a nanofiltration membrane (Desal 5 DK) removes bisphenol A (BPA) was investigated, together with the mechanisms involved. Whereas high retention (>90%) was obtained at the beginning of the filtration, the observed retention coefficient (R_obs) decreased to around 50% when the membrane became saturated, due to adsorption of BPA onto the membrane structure. The presence of ions (Na⁺, Cl⁻) affects the R_obs, this effect being attributed to a change in BPA hydrodynamic radius. Moreover, in our operating conditions, the presence of natural organic matter (1 mg/L) in the feed solution does not lead to variation in BPA retention at steady state.     

Strength performance of laterized concrete

The results of an experimental program to investigate some characteristics of concrete containing laterite as a partial or full replacement of sand is presented in this paper. Sand in a concrete of mix ratio 1:2:4:0.56 (cement:sand:coarse aggregate:water-cement ratio) was replaced with 0%, 20%, 40%, 60%, 80%, and 100% laterite. The results show that concrete with up to 40% replacement level of sand by laterite attained the designed strength of 20 N/mm², thus indicating the possibility of using laterite as a partial replacement for sand up to this level. It was also observed from the results that the workability of laterite concrete (LATCON) increases with increase in the replacement level of sand by laterite, while the compressive, split tensile, and flexural strengths and the percentage water absorption of the concrete decrease with increase in the replacement level of sand. Regression models relating the strengths of LATCON are also presented in this paper.     

Estimate of treatment plant effluent impact on chloride concentrations and oyster environment within the murderkill river estuary

The Murderkill River is a partially tidal body of water with summer-time 50-percentile freshwater flows ranging from 17.9 to 27.6ft³s⁻¹ (0.5 to 0.77m³s⁻¹) at a point coincident with the effluent discharge from the Kent County Regional Wastewater Treatment Plant (start-up late 1972). Chloride concentrations were determined over six summers to characterize river conditions prior to start-up of the 10-million gal day⁻¹ (37.850 m³ day⁻¹) (design) plant. Use of a one-dimensional steadystate model for a conservative substance shows that chloride values would be reduced by up to 20% at low water slack (LWS) periods for wastewater flows of 10 million gal day⁻¹ (37,850 m³ day⁻¹). The LWS chloride concentrations in the area of oyster production would be reduced to 3–6 ppt (5.9–10.8 ppt salinity) for wastewater loadings greater than 10 million gal day⁻¹ (37,850 m³ day⁻¹) . It is suggested that chloride additions in the treatment plant effluent be implemented to maintain minimum summertime low-water-slack levels of 5.6 ppt chloride (10 ppt salinity), consistent with a proper environment for oyster development.     

Influence of method and duration of curing and of mix proportions on strength of concrete containing laterite fine aggregate

In this paper, the influence of six curing methods (water, air, moist soil, jute bag, air/water and water/air) on the compressive strength of concrete cube specimens that contain laterite fine aggregate is investigated. Three different mixes of cement, laterite and gravel were used: ; 1:2:4 and 1:3:6 with water/cement ratios of 0.62, 0.75 and 1.02 by weight respectively. Four curing ages of 7, 14, 21 and 28 days were adopted. The results showed that the strength that a particular mix can attain is affected by the curing method used. The water/air curing technique gave the highest strength values of 28.2 Nmm⁻² for Nmm⁻² and 17.4 Nmm⁻² for 1:2:4 and 1:3:6 mixes respectively, while the air-cured specimens gave the lowest strength values of 17.2 Nmm⁻² for Nmm⁻² and 8.0 Nmm⁻² for 1:2:4 and 1:3:6 mixes. The higher the cement/aggregate ratio the higher the strength. Generally, there was increase in strength with age irrespective of the mix and the curing technique.     

Adsorbent obtained from CEPT sludge in wastewater chemically enhanced treatment

Chemically enhanced primary treatment (CEPT) in municipal wastewater treatment is particularly suitable for rapidly growing cities. The focus on CEPT process now might be the cost of chemicals and disposal of chemical sludge. In this study, the potential application of adsorbent made from CEPT sludge in CEPT wastewater treatment was investigated in various conditions, such as the adsorbent dosage, pH, and dosing modes of ferric chloride and adsorbent. It was found that sludge-derived adsorbent was a good way of sludge disposal while enhanced pollutants removal rate and reduced the fresh ferric chloride dosage. With the use of 10.0 mg L⁻¹ of ferric chloride and 0.6 g L⁻¹ of the adsorbent at the first stage simultaneously, the enhanced removal efficiencies of turbidity, UV₂₅₄, COD, TP were 83.3%, 52.3%, 48.8% and 89.0%, respectively. The experiments showed that ferric chloride dose was reduced about 50%. The pH played a significant role in coagulation and adsorption process.     

海砂混凝土耐久性能研究

通过海砂混凝土不同条件下力学性能和耐久性的测试,对海砂高强混凝土中的钢筋锈蚀能力进行了研究。结果表明,海砂中氯离子含量在0.123%、在混凝土中使用量低于320kg/m3的条件下,对强度高于50MPa的混凝土立方体抗压强度、碳化性能、抗氯离子扩散性能影响不大;海砂混凝土的钢筋锈蚀失重率随着海砂掺量的增加和水胶比的增大而增加;阻锈剂的掺入和保护层厚度的增加,可使海砂混凝土的抗钢筋锈蚀能力有所改善,钢筋锈蚀程度有所下降。     

Anaerobic biological treatment of phenol at 9.5-15 degrees C in an expanded granular sludge bed (EGSB)-based bioreactor

The aims of this study were to demonstrate the (1) feasibility of psychrophilic, or low-temperature, anaerobic digestion (PAD) of phenolic wastewaters at 10–15 °C; (2) economic attractiveness of PAD for the treatment of phenol as measured by daily biogas yields and (3) impact on bioreactor performance of phenol loading rates (PLRs) in excess of those previously documented (1.2 kg phenol m⁻³ d⁻¹). Two expanded granular sludge bed (EGSB)-based bioreactors, R1 and R2, were employed to mineralise a volatile fatty acid-based wastewater. R2 influent wastewater was supplemented with phenol at an initial concentration of 500 mg l⁻¹ (PLR, 1 kg m⁻³ d⁻¹). Reactor performance was measured by chemical oxygen demand (COD) removal efficiency, CH₄ composition of biogas and phenol removal (R2 only). Specific methanogenic activity, biodegradability and toxicity assays were employed to monitor the physiological capacity of reactor biomass samples. The applied PLR was increased to 2 kg m⁻³ d⁻¹ on day 147 and phenol removal by day 415 was 99% efficient, with 4 mg l⁻¹ present in R2 effluent. The operational temperature of R1 (control) and R2 was reduced by stepwise decrements from 15 °C through to a final operating temperature of 9.5 °C. COD removal efficiencies of c. 90% were recorded in both bioreactors at the conclusion of the trial (day 673), when the phenol concentration in R2 effluent was below 30 mg l⁻¹. Daily biogas yields were determined during the final (9.5 °C) operating period, when typical daily R2 CH₄ yields of c. 3.3 l CH₄ g⁻¹ COD_removed d⁻¹ were recorded. The rate of phenol depletion and methanation by R2 biomass by day 673 were 68 mg phenol g VSS⁻¹ d⁻¹ and 12–20 ml CH₄ g VSS⁻¹ d⁻¹, respectively.     

Effect of temperature on the residual compressive strength of laterized concrete

Tests are reported on 100 mm laterized concrete cubes, containing ordinary portland cement, crushed granite, sharp sand and fine laterite in varying proportions. The percentage of sand by weight of total fine aggregate was varied in steps of 25% up to a maximum of 100% corresponding to normal concrete. The mix proportion was . The test specimens were exposed to varying temperatures ranging from 30°C (i.e. room temperature) to 800°C and allowed to cool for 24 hours before crushing. The results showed that unlike normal concrete the residual compressive strength of laterized concrete increaed, by up to 50% of the nominal strength, with increasing temperature up to 200°C before falling to about 20% of the nominal strength at 800°C. The gain in strength depended on the sand content. The results further showed that within the limits of water/cement ratios normally used in concrete works (i.e. 0.55 to 0.65), the residual strength of laterized concrete was independent of the water/cement ratio. Also, the density of laterized concrete was not significantly affected by changes in temperature but that the tangent modulus of elasticity was reduced from 18 kN/mm² at 30°C to 0.12 kN/mm² at 600°C.     

Sorption of cadmium(II) and zinc(II) ions from aqueous solutions by cassava waste biomass (Manihot sculenta Cranz)

The sorption of two divalent metal ions, Cd(II) and Zn(II), onto untreated and differentially acid-treated cassava waste biomass over a wide range of reaction conditions was studied at 30°C. The metal ion removal from the spent biomass was also measured. The batch experiments show that pH 4.5–5.5 was the best range for the sorption of the metal ions for untreated and acid-treated biomass. Time-dependent experiments for the metal ions showed that for the two metals examined, binding to the cassava waste biomass was rapid and occurred within 30 min and completed within 1 h. High sorption capacities were observed for the two metals. The binding capacity experiments revealed the following amounts of metal ions bound per gram of biomass: 86.68 mg/g Cd, 55.82 mg/g Zn and 647.48 mg/g Cd, 559.74 mg/g Zn for untreated and acid-treated biomass, respectively. It was further found that the rate of sorption was particle-diffusion controlled, and the sorption rate coefficients were determined to be 2.30×10⁻¹ min⁻¹ (Cd²⁺), 4.0×10⁻³ min⁻¹ (Zn²⁺) and 1.09×10⁻¹ min⁻¹ (Cd²⁺), 3.67×10⁻² min⁻¹ (Zn²⁺) for 0.5 and 1.00 M differential acid treatment, respectively. Desorption studies showed that acid treatment inhibited effective recovery of metal ions already bound to the biomass as a result of stronger sulfhydryl-metal bonds formed. Less than 25% of both metals were desorbed as concentration of acid treating reagent increases. However, over 60% Cd and 40% Zn were recovered from untreated biomass during the desorption study. The results from these studies indicated that both untreated and acid-treated cassava waste biomass could be employed in the removal of toxic and valuable metals from industrial effluents.     

The long-term nutrient accumulation with respect to anthropogenic impacts in the sediments from two freshwater marshes (Xianghai Wetlands, Northeast China)

Sediment cores, representing a range of watershed characteristics and anthropogenic impacts, were collected from two freshwater marshes at the Xianghai wetlands (Ramsar site no. 548) in order to trace the historical variation of nutrient accumulation. Cores were ²¹⁰Pb- and ¹³⁷Cs-dated, and these data were used to calculate sedimentation rates and sediment accumulation rates. Ranges of dry mass accumulation rates and sedimentation rates were 0.27–0.96 g m⁻² yr⁻¹ and 0.27–0.90 cm yr⁻¹, respectively. The effect of human activities on increased sediment accumulation rates was observed. Nutrients (TOC, N, P, and S) in sediment were analyzed and nutrient concentration and accumulation were compared in two marshes with different hydrologic regime: an “open” marsh (E-0) and a partly “closed” marsh (F-0). Differences in physical and chemical characteristics between sediments of “open” and partly “closed” marsh were also observed. The “open” marsh sequestered much higher amounts of TOC (1.82%), N (981.1 mg kg⁻¹), P (212.17 mg kg⁻¹), and S (759.32 mg kg⁻¹) than partly “closed” marsh (TOC: 0.32%, N: 415.35 mg kg⁻¹, P: 139.64 mg kg⁻¹, and S: 624.45 mg kg⁻¹), and the “open” marsh indicated a rather large historical variability of TOC, N, P, and S inputs from alluvial deposits. Nutrient inputs (2.16–251.80 g TOC m⁻² yr⁻¹, 0.43–20.12 g N m⁻² yr⁻¹, 0.39–3.03 g P m⁻² yr⁻¹, 1.60–15.13 g S m⁻² yr⁻¹) into the Xianghai wetlands of China are in the high range compared with reported nutrient accumulation rates for freshwater marshes in USA. The vertical variation, particularly for N, P, and S indicated the input history of the nutrients of the Xianghai wetlands developed in three periods—before 1950s, 1950–1980s, and after 1980s. The ratios between anthropogenic and natural inputs showed that the relative anthropogenic inputs of TOC, N, P, and S have been severalfold (TOC: 1.68–11.21, N: 0.47–3.67, P: 0.24–1.36, and S: 1.46–2.96) greater than values of their natural inputs after 1980s. The result is probably attributable, in part, to two decades of surface coal mining activities, urban sewage, and agriculture runoff within the upstream region of the Huolin River. Our findings suggest that the degree of anthropogenic disturbance within the surrounding watershed regulates wetland sediment, TOC, N, P, and S accumulation.     

机制砂中石粉对混凝土耐久性的影响研究

试验研究了石粉含量对不同强度等级机制砂混凝土强度、抗氯离子渗透性能和抗冻性能的影响。结果表明:石粉对低强和高强混凝土的影响不完全相同,对于低强度机制砂混凝土,随着机制砂中石粉含量的增加,混凝土的抗氯离子渗透性能提高,而抗冻性能降低,尤其是当石粉含量高于10%(石粉与水泥体积比超过1∶3.47)时,混凝土劣化明显;但对于高强混凝土而言,仅当石粉含量大于7%时,石粉使混凝土工作性出现劣化,而对于抗氯离子渗透性能,抗冻性能等耐久性,石粉含量从3.5%提高到14%,均未使高强机制砂混凝土出现劣化现象。     

Anaerobic digestion of wine distillery wastewater in down-flow fluidized bed

In down-flow fluidization, particles with a specific density smaller than the liquid are fluidized downward by a concurrent flow of liquid. This paper describes the application of the down-flow (or inverse) fluidization technology for the anaerobic digestion of red wine distillery wastewater. The carrier employed was ground perlite, an expanded volcanic rock. Before starting-up the reactor, physical and fluidization properties of the carrier material were determined. 0.968 mm perlite particles were found to have a specific density of 280 kg m⁻³ and a minimum fluidization velocity of 2.3 m h⁻¹. Once the down-flow anaerobic fluidized bed system reached the steady-state, organic load was increased stepwise by reducing HRT, from 3.3–1.3 days, while maintaining constant the feed TOC concentration. The system achieved 85% TOC removal, at an organic loading rate of 4.5 kg TOC m³ d⁻¹. It was found that the main advantages of this system are: low energy requirement, because of the low fluidization velocities required; there is no need of a settling device, because solids accumulate at the bottom of the reactor so they can be easily drawn out, and particles with high-biomass content, whose specific density have become larger than 1000 kg m⁻³ can be easily recovered.     

Effect of electrolyte composition, and of added iron(III) in the presence of selected organic complexing agents, on nickel(II) precipitation by lime

The effect of effluent composition involving the common anionic species Cl⁻, SO₄²⁻ and CO₃²⁻ on the efficiency of nickel(II) precipitation, modelling lime (CaO) as the precipitant, has been investigated using the solubility domain approach. Solubility domains were based on the phases that were found to limit metal solubility for systems representing potential effluent composition limits. These phases were found to resemble their mineralized counterparts, but with a lower degree of structural order. At higher SO₄²⁻ and CO₃²⁻ concentrations both gypsum (CaSO₄·2H₂O) and calcite (CaCO₃) were formed, but these had little effect on the observed residual nickel solubility. The calculated solubility domains were found to generally encompass the experimentally determined solubilities, thereby providing quality assurance ranges for hydroxide precipitation. The effect of the complexing anions tartrate and EDTA⁴⁻ on residual Ni(II) in solution as well as the effects of the addition of Fe(III) on the removal of Ni(II) complexed by these species are described.     

Cadmium and lead in selected tissues of two commercially important fish species from the Adriatic Sea

Baseline levels of cadmium and lead were determined in muscle tissue and liver of hake (Merluccius merluccius) and red mullet (Mullus barbatus), two commercially important fish species from the eastern Adriatic. Concentrations of trace metals in liver (Cd: 6–183 μg kg⁻¹ w. wt. ; Pb: 39–970 μg kg⁻¹ w. wt.) were within the range of recently published data for the Mediterranean. In the muscle tissue, cadmium concentrations (4.1–29 μg kg⁻¹ w. wt.) were among the lowest reported values for the Mediterranean, whereas lead levels (49–158 μg kg⁻¹ w. wt.) were within the range of values reported for various coastal areas of the Mediterranean. Presented data on cadmium and lead content in the studied fish species provide no proof of the general pollution of the Adriatic. Obtained data were tested in relation to fish length. Metal concentrations in liver decreased with the increase in fish size, whereas no significant correlation was found between trace metal levels in the muscle tissue and the length of both species. Relationships between metal concentrations and sex were also tested, but they gave no significant results. A comparison of contaminant concentrations in the edible tissue of hake and red mullet with the Croatian legislation shows that the consumption of their meat is not harmful for humans, not even for the most endangered population from the coastal region.     

混凝土不同层次结构抗氯盐侵蚀性能与相互关系的研究

针对混凝土多层次结构(水泥浆、砂浆和混凝土三个层次结构)的特点,试验研究了混凝土不同层次结构的抗氯盐侵蚀性能及相互关系.研究结果表明:混凝土中三个层次的抗氯盐侵蚀性能按净浆、砂浆和混凝土的次序增强,高性能混凝土配合比设计应控制三个层次比例,控制浆骨比、砂胶比和砂率等配合比参数,保证混凝土具有较高的抗氯盐侵蚀性能.