Comparative study of efficiencies of purification of cadmium contaminated irrigation water by different purification systems

Cadmium (Cd) contamination in rice threats food safety and human health. Control of Cd pollution has become an urgent need. Most existing studies on heavy metal pollution control have focused on industrial wastewater and few on irrigation water. Some researchers have found ecological ditches, plant ponds and constructed wetlands have the potential of treating heavy metal contaminated irrigation water, but they examined only one of the methods and the validity needs to be verified by field studies. Our study has filled the gap by combining the methods and using field experiments. We examined efficiencies of removal of Cadmium from irrigation water by 14 different combinations of ecological ditches, plant ponds, and constructed wetlands using field experiments. The effects of the purification on Cd concentration in paddy soil and rice grains were also examined. Results showed that there were significant differences among efficiencies of purification of Cd contaminated irrigation water using different systems and that pH, chemical form of Cd in irrigation water, vegetation coverage and biomass of aquatic plants significantly affect the efficiency. Of the 14 purification systems, seven resulted in the concentration of Cd in the effluent water meeting the National Standard for Irrigation Water Quality (GB5084-2021) for all days of the experiment period. The highest amount and rate of Cd removal were achieved by the combination of two-stage ecological ditch, two-stage plant pond, and one-stage constructed wetland, while the highest removal amount and rate per 100 m2 was achieved by the combination of one-stage plant pond and one-stage constructed wetland. Considering purification efficiency, area of coverage, and cost of construction and maintenance, we suggest that combination of plant pond and constructed wetland be a priority choice for purification of Cd pollution in irrigation water. Compared to the control data collected from rice grain and paddy soil irrigated by unpurified water, Cd concentration in rice grain and paddy soil irrigated by purified water declined by 5.08-19.42 % and 30.93-77.15 % respectively. All results showed that removal of Cd contamination from irrigation water effectively controlled cadmium pollution in rice grain and paddy soil. Our study not only contributes to pollution control practice, but also warrants further investigation of the mechanisms of how the treatment systems work. The most efficient method we identified could be applied locally, regionally and in areas of similar topography, climate, soil, vegetation, agriculture, and heavy metal pollution.

Effects of regular zooplankton supplement on the bacterial communities and process performance of biofilm for wastewater treatment

Biofilm processing technologies were widely used for wastewater treatment due to its advantages of low cost and easy management. However, the aging biofilms inevitably decrease the purification efficiency and increase the sludge production, which limited the widely application of biofilms technologies in rural area. In this study, we proposed a novel strategy by introducing high-trophic organisms to prey on low-trophic organisms, and reduce the aged biofilms and enhance treatment efficiencies in rural wastewater treatment. The effect of three typical zooplankton (Paramecium, Daphnia, and Rotifer) supplement on the purification efficiency and biofilm properties in the contact oxidation process were investigated, and the reaction conditions were optimized by an orthogonal experiment. Under optimal conditions, the biofilms weight decreased 67.6%, the oxygen consumption rate of biofilms increased 9.4%, and wastewater treatment efficiency was obviously increased after zooplankton supplement. Microbial sequencing results demonstrated that the zooplankton optimize the contact oxidation process by altering the bacterial genera mainly Diaphorobacter, Thermomonas, Alicycliphilus and Comamonas. This research provides insight into mechanism of the zooplankton supplement in biological contact oxidation process and provides a feasible strategy for improving the rural sewage treatment technology.

Emission and purification of evaporated-condensed oil droplets affected by condensation nuclei during machining

Fine oil droplets emitted by evaporation-condensation during machining are typical indoor air contaminants. Airborne particles can act as condensation nuclei, facilitating the condensation of oil vapor. The physical properties of these resultant droplets significantly affect their purification efficiency. Herein, this study aimed to elucidate the emission characteristics of oil droplets formed by evaporation-condensation affected by condensation nuclei and the purification efficiency of intense field dielectric (IFD) technology for the droplets under varying airflow velocities. Results show that the removal of condensation nuclei can effectively reduce the mass of evaporated-condensed oil droplets, and the increment in the mass of oil droplets reached 1.7 times the increment in the mass of condensation nuclei. It was more effective to reduce the mass of oil droplets by removing large condensation nuclei and decreasing the amount of evaporated soluble oil, as compared to removing smaller condensation nuclei or using straight oil. Condensation nuclei mainly contributed to the generation of oil droplets below 5 µm. For droplet diameters of 0.3-5.0 µm and airflow velocities of 0.5-2.0 m/s, the purification efficiency was within the 84-96% range. The purification efficiency of the IFD purifier for oil droplets could be improved either by increasing the size of the oil droplets or by reducing the airflow velocity.

Chemical characterization of volatile organic compounds (VOCs) emitted from multiple cooking cuisines and purification efficiency assessments

Cooking process can produce abundant volatile organic compounds (VOCs), which are harmful to environment and human health. Therefore, we conducted a comprehensive analysis in which VOCs emissions from multiple cuisines have been sampled based on the simulation and acquisition platform, involving concentration characteristics, ozone formation potential (OFP) and purification efficiency assessments. VOCs emissions varied from 1828.5 to 14,355.1 µg/m³, with the maximum and minimum values from Barbecue and Family cuisine, respectively. Alkanes and alcohol had higher contributions to VOCs from Sichuan and Hunan cuisine (64.1%), Family cuisine (66.3%), Shandong cuisine (69.1%) and Cantonese cuisine (69.8%), with the dominant VOCs species of ethanol, isobutane and n-butane. In comparison, alcohols (79.5%) were abundant for Huaiyang cuisine, while alkanes (19.7%), alkenes (35.9%) and haloalkanes (22.9%) accounted for higher proportions from Barbecue. Specially, carbon tetrachloride, n-hexylene and 1-butene were the most abundant VOCs species for Barbecue, ranging from 8.8% to 14.6%. The highest OFP occurred in Barbecue. The sensitive species of OFP for Huaiyang cuisine were alcohols, while other cuisines were alkenes. Purification efficiency assessments shed light on the removal differences of individual and synergistic control technologies. VOCs emissions exhibited a strong dependence on the photocatalytic oxidation, with the removal efficiencies of 29.0%-54.4%. However, the high voltage electrostatic, wet purification and mechanical separation techniques played a mediocre or even counterproductive role in the VOCs reduction, meanwhile collaborative control technologies could not significantly improve the removal efficiency. Our results identified more effective control technologies, which were conductive to alleviating air pollution from cooking emissions.

Nutrient removal from biogas slurry and biogas upgrading by microalgae-fungi-bacteria co-cultivation under different carbon nanotubes concentration

In this study, Chlorella vulgaris, Ganoderma lucidum, and endophytic bacteria were co-cultivated with the stimulation of strigolactone analogs GR24 to prepare pellets. During the purification of biogas slurry and biogas, multi-walled carbon nanotubes (MWCNTs) were introduced to enhance the removal efficiencies of nutrients and CO₂. The results showed that both GR24 and MWCNTs affected the purification of biogas slurry and biogas. The maximum chemical oxygen demand, total nitrogen, total phosphorus, and CO₂ removal efficiencies of the Chlorella vulgaris-Ganoderma lucidum-endophytic bacterial symbionts were 82.57 ± 7.96% (P < 0.05), 82.14 ± 7.87% (P < 0.05), 84.27 ± 7.96% (P < 0.05), and 63.93 ± 6.22% (P < 0.05), respectively, with the induction of 10^-9 M GR24 and 1 mg L^-1 MWCNTs. Moreover, the growth and photosynthetic performance of the symbionts were consistent with the removal effects. The Chlorella vulgaris-Ganoderma lucidum-endophytic bacterial symbionts obtained high growth rates and enzyme activity with the maximum growth rate of 0.365 ± 0.03 d^-1, mean daily productivity of 0.182 ± 0.016 g L^-1 d^-1, and carbonic anhydrase activity of 31.07 ± 2.75 units, respectively. These results indicated that an appropriate concentration of GR24 and MWCNTs could promote the growth of symbionts, reinforce the purification effects of biogas slurry and biogas, and provide a new idea for the simultaneous purification of wastewater and biogas.

A review on the treatment of dyes in printing and dyeing wastewater by plant biomass carbon

Printing and dyeing wastewater (PDW) has characteristics of large amount of water, elevated content of residual dyes, poor biodegradability, high alkalinity and large change of water quality, making its treatment difficult. Development of efficient and economic PDW treatment technology has gained considerable interest in the field of environmental protection. Use of plant biomass carbon (PBC) for the adsorption of dyes is a feasible and economical technology. This review summarizes current literature discussing the preparation method and physicochemical characteristics of PBC prepared from different plant species, the effect of PBC on the removal of dyes, influencing factors affecting the removal, and relevant adsorption models. The shortcomings of current research and the direction of future research are also pointed out in the review.

Ecological floating bed for decontamination of eutrophic water bodies: Using alum sludge ceramsite

In this study, a combined ecological floating bed (C-EFB) with alum sludge ceramsite (ASC) was designed to improve the water purification effect of traditional ecological floating beds (T-EFBs). During the ASC preparation stage, alum sludge was shaped into a ball, air-dried, and fired under 600 °C. The physical and chemical properties of the ASC meet the requirements of Artificial Ceramsite Filter Materials for Water Treatment (CJ/T229-2008). This study investigated the increased capability of this new-type artificial substrate (ASC) on the removal of chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total phosphorus (TP), and total nitrogen (TN) from eutrophic landscape water. Compared with the T-EFB, the C-EFB owns a higher purification efficiency. The highest average efficiency of COD, NH4+-N, TN and TP removals during the four operating stages was 78.2%, 58.1%, 46.7% and 53.2%, respectively, in the C-EFB, which were all higher than those of 53.5%, 32.4%, 27.2% and 25.8%, respectively, for the T-EFB. Among them, the C-EFB showed a higher advantage in the removal of TP. The results showed that the potential benefits of utilizing ASC in seriously eutrophic bodies of water.

Photocatalytic purification of vehicle exhaust using CeO2-Bi2O3 loaded on white carbon and tourmaline

Photocatalysts are environmentally friendly materials that can be used to degrade vehicle exhaust. CeO₂-Bi₂O₃ loaded on white carbon and tourmaline, as the favorable absorption materials, was prepared respectively for vehicle exhaust photocatalytic purification. Brunauer-Emmett-Teller (BET) adsorption isotherm, scanning electron microscope (SEM), Fourier transform infrared (FTIR), X-ray diffraction (XRD), transmission electron microscope (TEM), and X-ray photoelectron spectroscopy (XPS) were applied to characterize the composite materials. The optimum contents of the loading materials were obtained from the comparison of purification efficiency of vehicle exhaust components after a 60-min photocatalytic reaction under visible and ultraviolet (UV) irradiation, including hydrocarbons (HC), carbon monoxide (CO), carbon dioxide (CO₂), and nitrogen oxides (NO_x). The results show that the proposed preparation method could improve particle dispersion and distribution uniformity, reduce particle agglomeration, and increase specific surface area. The optical response range of the CeO₂-Bi₂O₃ with loading materials can be extended from UV light to visible light. CeO₂-Bi₂O₃ loaded on tourmaline show excellent photocatalytic purification effect under visible light. The purification efficiency of CeO₂-Bi₂O₃ loaded on tourmaline for HC, CO, CO₂, and NO_x were 30.8%, 30.6%, 35.3%, and 47.6%, respectively. Moreover, the concentrations of vehicle exhaust components decrease with time, which is well fitted by the Langmuir-Hinshelwood pseudo-first-order kinetics model, and the purification rate constant of CeO₂-Bi₂O₃ composites under visible light is greater than that under UV light. The prepared photocatalytic materials also exhibit the excellent reusability.

Effect of Arthrospira platensis microalgae protein purification on emulsification mechanism and efficiency

In light of environmental concerns and changing consumer demands, efforts are increasing to replace frequently used animal-based emulsifiers. We demonstrate the interfacial network formation and emulsifying potential of Arthrospira platensis protein extracts and hypothesize a mechanistic change upon progressing purification. A microalgae suspension of A. platensis powder in phosphate buffer solution (pH 7, 0.1 M) was homogenized and insoluble components separated by centrifugation. Proteins were precipitated at the identified isoelectric point at pH 3.5 and diafiltrated. In interfacial shear rheology measurements, the build-up of an interfacial viscoelastic network was faster and final network strength increased with the degree of purification. It is suggested that isolated A. platensis proteins rapidly form an interconnected protein layer while coextracted surfactants impede protein adsorption for crude and soluble extracts. Emulsions with 20 vol % medium chain triglycerides (MCT) oil could be formed with all extracts of different degrees of purification. Normalized by protein concentration, smaller droplets could be stabilized with the isolated fractions. For potential applications in food, pharma and cosmetic product categories, the enhanced functionality has to be balanced against the loss in biomass while purifying microalgae proteins or other alternative single cell proteins.

Removal of metals from mine drainage waters by in situ mineral sorbent-based pilot filter systems

Discharge of metal-containing wastewater streams into the environment is an environmental concern because these pollutants do not degrade and tend to bioaccumulate. A number of laboratory-based investigations on the effectiveness of a wide range of filter materials for metal removal from diluted wastewater streams have been reported. However, only a few pilot or full-scale investigations have been conducted. Therefore, this study investigated the metal retention capabilities of mineral-based filter materials (commercially available mineral product (5-15 mm), recycled mineral material (2-4 mm) and slag by-product (2-4 and 4-16 mm)) when used in pilot-scale filter systems under continuous operation in a closed mining area in North Ostrobothnia, Finland, between June and October 2017. The influence of material particle size on system function and on metal retention efficiency was also evaluated. The results revealed that system performance was dependent on material composition and particle size (smaller particle size being more effective). The highest metal removal efficiencies (Zn, Ni, Cd, Cu and Pb) and largest amount of water treated (per volume of material applied) were achieved by an aluminium oxide-based recycled mineral material (2-4 mm). While smaller-grained materials performed better in terms of removal efficiency, the removal rates achieved by coarser-grained, commercially available mineral product (5-15 mm) were comparable to those achieved by small-grained slag (2-4 mm). Full-scale systems using the recycled mineral product (2-4 mm) would have an approximately two-fold longer material replacement time than systems using the slag (2-4 mm). Replacement time for the larger-grained materials tested could not be determined, due to problems with freezing. Overall, the recycled mineral material tested can be recommended for full-scale tests, especially when high zinc removal rates are required.

Correlation Among Soil Enzyme Activities, Root Enzyme Activities, and Contaminant Removal in Two-Stage In Situ Constructed Wetlands Purifying Domestic Wastewater

Two-stage in situ wetlands (two vertical flow constructed wetlands in parallel and a horizontal flow constructed wetland) were constructed for studying domestic wastewater purification and the correlations between contaminant removal and plant and soil enzyme activities. Results indicated the removal efficiency of NH4 (+) and NO3 (-) were significantly correlated with both urease and protease activity, and the removal of total phosphorus was significantly correlated with phosphatase activity. Chemical oxygen demand removal was not correlated with enzyme activity in constructed wetlands. Plant root enzyme (urease, phosphatase, protease and cellulose) activity correlation was apparent with all contaminant removal in the two vertical flow constructed wetlands. However, the correlation between the plant root enzyme activity and contaminant removal was poor in horizontal flow constructed wetlands. Results indicated that plant roots clearly played a role in the removal of contaminants.