Performance of a Constructed Wetland and Pretreatment System Receiving Potato Farm Wash Water

Insights into carbon-neutral treatment of rural wastewater by constructed wetlands: A review of current development and future direction

In recent years, with the global rise in awareness regarding carbon neutrality, the treatment of wastewater in rural areas is increasingly oriented towards energy conservation, emission reduction, low-carbon output, and resource utilization. This paper provides an analysis of the advantages and disadvantages of the current low-carbon treatment process of low-carbon treatment for rural wastewater. Constructed wetlands (CWs) are increasingly being considered as a viable option for treating wastewater in rural regions. In pursuit of carbon neutrality, advanced carbon-neutral bioprocesses are regarded as the prospective trajectory for achieving carbon-neutral treatment of rural wastewater. The incorporation of CWs with emerging biotechnologies such as sulfur-based autotrophic denitrification (SAD), pyrite-based autotrophic denitrification (PAD), and anaerobic ammonia oxidation (anammox) enables efficient removal of nitrogen and phosphorus from rural wastewater. The advancement of CWs towards improved removal of organic and inorganic pollutants, sustainability, minimal energy consumption, and low carbon emissions is widely recognized as a viable low-carbon approach for achieving carbon-neutral treatment of rural wastewater. This study offers novel perspectives on the sustainable development of wastewater treatment in rural areas within the framework of achieving carbon neutrality in the future.

Effects of coagulation pre-treatment on chemical and microbial properties of water-soil-plant systems of constructed wetlands

Chemical coagulation has gained recognition as an effective technique to enhance the removal efficiency of pollutants in wastewater prior to their entry into a constructed wetland (CW) system. However, its potential impact on the chemical and microbial properties of soil and plant systems within CWs requires further research. This study investigated the impact of using ferric chloride (FeCl3) as a pre-treatment stage for dairy wastewater (DWW) on the chemical and microbial properties of water-soil-plant systems of replicated pilot-scale CWs, comparing them to CWs treating untreated DWW. CWs treating amended DWW had better performance than CWs treating raw DWW for all water quality parameters (COD, TSS, TP, and TN), ensuring compliance with the EU wastewater discharge directives. Soil properties remained mostly unaffected except for pH, calcium and phosphorus (P), which were lower in CWs treating amended DWW. As a result of lower nitrogen (N) and P loads, the plants in CWs receiving FeCl3-amended DWW had lower N and P contents than the plants of raw DWW CWs. However, the lower loads of P into amended DWW CWs did not limit the growth of Phragmites australis, which were able to accumulate trace elements higher than CWs receiving raw DWW. Alpha and Beta-diversity analysis revealed minor differences in community richness and composition between both treatments, with only 3.7% (34 genera) showed significant disparities. Overall, the application of chemical coagulation produced superior effluent quality without affecting the properties of soil and plant of CWs or altering the functioning of the microbial community.

Recent advances and prospects of constructed wetlands in cold climates: a review from 2013 to 2023

Constructed wetland (CW), a promising, environmentally responsible, and effective green ecological treatment technology, is actively involved in the treatment of various forms of wastewater. Low temperatures will, however, lead to issues including plant dormancy, decreased microbial activity, and ice formation in CWs, which will influence how well CWs process wastewater. Applying CWs successfully and continuously in cold areas is extremely difficult. Therefore, it is crucial to find solutions for the pressing issue of increasing the CWs' ability to process wastewater at low temperatures. This review focuses on the effect of cold climate on CWs (plants, substrates, microorganisms, removal effect of pollutants). It meticulously outlines current strategies to enhance CWs' performance under low-temperature conditions, including modifications for the improvement and optimization of the internal components (i.e., plant and substrate selection, bio-augmentation) and enhancement of the external operation conditions of CWs (such as process combination, effluent recirculation, aeration, heat preservation, and operation parameter optimization). Finally, future perspectives on potential research directions and technological innovations that could strengthen CWs' performance in cold climates are prospected. This review aims to contribute valuable insights into the operation strategies, widespread implementation, and subsequent study of CWs in colder climate regions.

Life cycle assessment for the land application of food processing wash-water and solid residuals

A life cycle assessment (LCA) study was completed to understand the environmental impacts associated with the land application of wastes produced from rural food-processing operations for final disposal. The system boundaries for the two comprised scenarios included the storage of the produced non-agriculture source material (NASM), transportation to an applicable location, land application of the NASM, and the impacts of the final emissions to the soil and groundwater for a full year. The Tool for the Reduction and Assessment of Chemicals and Other Environmental Impacts (TRACI) v2.1 was selected as the impact assessment method. Furthermore, SimaPro 8.0.4.26 was the LCA model version that was used with all the databases included. Overall, the LCA study showed that the most significant environmental impacts associated with the disposal process resulted from carcinogenic and eutrophication emissions. The component that contributed the most to carcinogenic impacts was found to be from the material required to create the concrete storage tank. Additionally, eutrophication was identified to be a potential significant impact, if proper setback requirements are not followed for the NASM material. Results of the study look to inform stakeholders about the benefits and risks encountered from NASM disposal. PRACTITIONER POINTS: Life cycle assessment was completed on a representative NASM disposal system using land application. Concrete tank used for storage of NASM had the most significant impact in carcinogenic emissions. Eutrophication impacts were the second most significant impact behind carcinogenic emissions.

Free water surface constructed wetlands: review of pollutant removal performance and modeling approaches

Free water surface constructed wetlands (FWSCWs) for the treatment of various wastewater types have evolved significantly over the last few decades. With an increasing need and interest in FWSCWs applications worldwide due to their cost-effectiveness and other benefits, this paper reviews recent literature on FWSCWs' ability to remove different types of pollutants such as nutrients (i.e., TN, TP, NH4-N), heavy metals (i.e., Fe, Zn, and Ni), antibiotics (i.e., oxytetracycline, ciprofloxacin, doxycycline, sulfamethazine, and ofloxacin), and pesticides (i.e., Atrazine, S-Metolachlor, imidacloprid, lambda-cyhalothrin, diuron 3,4-dichloroanilin, Simazine, and Atrazine) that may co-exist in wetland inflow, and discusses approaches for simulating hydraulic and pollutant removal processes. A bibliometric analysis of recent literature reveals that China has the highest number of publications, followed by the USA. The collected data show that FWSCWs can remove an average of 61.6%, 67.8%, 54.7%, and 72.85% of inflowing nutrients, heavy metals, antibiotics, and pesticides, respectively. Optimizing each pollutant removal process requires specific design parameters. Removing heavy metal requires the lowest hydraulic retention time (HRT) (average of 4.78 days), removing pesticides requires the lowest water depth (average of 0.34 m), and nutrient removal requires the largest system size. Vegetation, especially Typha spp. and Phragmites spp., play an important role in FWSCWs' system performance, making significant contributions to the removal process. Various modeling approaches (i.e., black-box and process-based) were comprehensively reviewed, revealing the need for including the internal process mechanisms related to the biological processes along with plants spp., that supported by a further research with field study validations. This work presents a state-of-the-art, systematic, and comparative discussion on the efficiency of FWSCWs in removing different pollutants, main design factors, the vegetation, and well-described models for performance prediction.

Recent technologies for nutrient removal and recovery from wastewaters: A review

Water scarcity and its pollution has become a concern in recent times. The disposal of nutrient-rich (nitrogen and phosphorous) wastewater is also one of the main cause of water pollution through eutrophication, reduced dissolved oxygen that poses threat to aquatic ecosystems. As a result, nutrient removal has become a mandate apart from the removal of organics. However, the removal of nutrients from sewage is a challenging task. Conversely, conventional biological treatment processes provide little relief in nutrient removal. The treated effluents from conventional biological processes do not achieve the stringent nutrient removal disposal standard limits and become primary cause of pollution in the receiving water bodies. This has stressed upon the need for eco-friendly, low-energy and cost-efficient nutrient removal treatment technologies. Various biological treatment combinations or variants are in use for the efficient removal of nutrients. The biological processes in itself or in combination with chemical processes are preferred over technologies based solely on physico-chemical processes for its treatment performance at lower cost. This review summarizes the existing treatment processes and their possible up-gradation with the aim to accomplish the marked effluent standards for the nutrients. The concept of conventional systems and advanced systems for nutrients (nitrogen and phosphorous) removal which are already developed or under development are deeply discussed. Further, the challenges of each treatment systems are abridged. Finally, the possible suggestions for the modification/retrofitting of existing treatment systems for achieving stringent disposal standards are pointed out.

A review on performance of constructed wetlands in tropical and cold climate: Insights of mechanism, role of influencing factors, and system modification in low temperature

Constructed wetlands (CWs) are one of the most promising and sustainable alternatives for wastewater treatment that are being successfully implemented in several countries, especially in tropical and sub-tropical regions. The predominant mechanisms of removal of contaminants in CWs are microbial degradation, phytodegradation, phytoextraction, filtration, sedimentation, and adsorption, etc. Vertical flow subsurface CWs and hybrid CWs demonstrated promising results in terms of TN, BOD, and COD removal, while horizontal flow subsurface CWs were proficient in removal of TP. The performance of the CWs depends upon a various factors, such as hydraulic loading rate, pH, dissolved oxygen, temperature, etc. Among these, low temperature had the most antagonistic effect on the performance of the CWs because freezing ambient temperature lead to ice formation, hydraulic imperfections, malfunctioning of biotic and abiotic components, etc. Over the past three decades, thousands of studies have been conducted involving treatment of wastewater using CWs, among which only few have addressed the issues and concerns of cold climate representing a significant research gap in this field. Furthermore, the performance of CWs in terms of TN, TP, and COD removal was significantly lower in cold climates than that in tropical and sub-tropical climates. In order to find suitable remedies to overcome the challenges faced in cold climate various modifications, such as incorporating greenhouse structure, providing insulating materials, bio-augmentation, identification of suitable macrophytes, etc., in around 20 different scenarios have been studied. Greenhouse construction led to 20% increase in removal of TN and COD, while plant collocation accounted for up to 18% increase in the removal of COD. Artificial aeration, insulation and bio-augmentation also enhanced the performance of the CWs in low temperatures.

A small-scale study of plant orientation in treatment performance of vertical flow constructed wetland in continuous flow

In constructed wetland (CW) ecology, plants play a vital role in wastewater treatment. The plants provide an adequate surface to various microorganisms, transfers oxygen and uptake nutrients to treat wastewater. This study deals with the treatment of greywater by using vertical flow constructed wetland system (VFCW). In the present study, two reactors were prepared for two different orientations in monoculture (S-1) and mixed culture (S-2) by using four types of macrophytes (Canna indica, Colocasia, Hymenocallis littoralis, and Phragmites australis). The reactors were operated in continuous mode for 90 days by maintaining the 10 mL/min flow rate and 1-day retention time. The mean removal efficiency of S-1 is 40.70, 33.69, 27.13, 48.17, 66.76, and 50.82% for ammonia, total kjeldahl nitrogen (TKN), phosphate, sulfate, turbidity, and chemical oxygen demand (COD), respectively. The mean removal efficiency of S-2 CW is 53.06, 34.54, 37.49, 48.64, 69.26, and 58.26% for ammonia, TKN, phosphate, sulfate, turbidity, and COD, respectively. ANOVA showed significant differences among both VFCWs in removal efficiency for all measured parameters. The performance of the two systems was compared with each other with the significance level of p = 0.05. The results indicated that the orientation of plant plays a major role in the removal of various physicochemical parameters.

Ecological floating bed (EFB) for decontamination of polluted water bodies: Design, mechanism and performance

Worldwide water quality is degrading and most of the water bodies are now being contaminated by heavy load of pollutants from various industries. Aquatic ecosystems are also disrupted affecting various flora and fauna adversely. Water bodies dominated with aquatic plants have high yielding capacity. These plants are capable of high nutrient accumulation and creating favorable condition in rhizosphere for microbial organic degradation, which can be applied in the restoration process of polluted lakes, natural streams and wetlands, etc. Ecological Floating Bed (EFB) is designed by using aquatic plants, floating like mat on the surface of water. The plant roots hang beneath the floating mat and provide a large surface area for biofilm growth. This paper reviewed the EFB concept, structure, mechanisms and functions. Screening of suitable macrophyte species, involvement of biofilm in organic removal process and necessity of growth media have been discussed briefly. Apart from this, effect of depth, buoyancy, vegetation coverage ratio are also represented. Detail mechanisms of oxygen transfer from top to bottom of water biomass have been well analyzed. Various pollutants present in wastewater like organics, solids, nitrogen, phosphorous, heavy metals etc. and their removal mechanism have also mentioned. Again biomass needs to be harvested in regular interval, else the absorbed nutrients may re-enter to the water body. Overall, EFB is an efficient and effective wastewater treatment technology and further research is necessary for its better utilization. Finally, based on reviews, recommendations have been made for future research.