Wetlands for wastewater treatment and subsequent recycling of treated effluent: a review

Alternative adsorbents applied to the removal of natural hormones from pig farming effluents and characterization of the biofertilizer

Pig farming has a very strong economic importance in Brazil. The residues from this activity are applied to the soil because of their excellent characteristics as biofertilizers. The present study aimed at studying the estrone, 17β-estradiol, and estriol natural hormones, emerging contaminants present in this type of residue that are not mentioned in the current legislation. The characterization of the pig farming effluent presented high concentrations of hormones (mg L-1). The objective was to apply the biosorbents to the removal of the hormones in batch systems directly in the manure heaps without affecting the potential of the effluent as a fertilizer. It was verified that the adsorption of hormones using the rice husk biomass in natura and soybean hull in natura, abundant alternative adsorbents, presented a good capacity of removal of hormones. The presence of the organic materials (rice husk and soybean hull) caused few alterations in the biofertilizer characteristics, demonstrating that these adsorbents present a potential of application in batch treatment systems, with possible applications related to pig farming effluents containing natural hormones.

Sustainability

This review on Sustainability covers selected 2018 publications on the focus of sustainability. It is divided into the following sections: (a) Water quantity; (b) Water quality; (c) Climate change and resilience; (d) Planning and ecosystem evaluation; (e) Life cycle assessment (LCA) applications; (f) Sustainable management; (g) Sustainability and asset management; (h) Sustainability in wastewater treatment; (i) Sustainable water and wastewater utilities; (j) Sustainable water resource management.

Water reclamation and reuse

Literature published in 2018 pertinent to water reclamation and reuse has been classified into five topics: safe reuse, treatment technologies, management, assessment, and case studies. Researches have been conducted to develop new technologies and improve conventional treatments for achieving sustainable wastewater reclamation, and increasing efforts have been made to facilitate safe water reuse. PRACTITIONER POINTS: The way of publicity greatly influences people's acceptance of water reuse and willingness to purchase produce irrigated with recycled water. Integrated process is the most commonly used treatment technology to reclaim water. There is a lack of local or regional regulatory and policy for sustainable water management.

The aeroponic rhizosphere microbiome: community dynamics in early succession suggest strong selectional forces

In the last decade there has been increased interest in the manipulation of rhizosphere microbial communities in soilless systems (hydroponics) through the addition of plant growth promoting microbes (PGPMs) to increase plant nutrition, lower plant stress response, and control pathogens. This method of crop management requires documenting patterns in communities living in plant roots throughout the growing season to inform decisions on timing of application and composition of the supplemental PGPM consortium. As a contribution to this effort, we measured changes in the bacterial community through early succession (first 26 days) in plant root biofilms growing in an indoor commercial aeroponic system where roots were sprayed with a mist of nutrient-amended water. By 12 days following seed germination, a root-associated community had established that was distinct from the source communities found circulating in the system. Successional patterns in the community over the following 2 weeks (12-26 days) included changes in abundance of bacterial groups that have been documented in published literature as able to utilize plant root exudates, release plant hormones, or augment nutrient availability. Six bacterial families/genera (Hydrogenophilaceae, Rhizobium, Legionellaceae, Methylophilus, Massilia, or Herbaspirillum) were the most abundant in each root sample, comprising 8-37% of the microbiome. Given the absence of soil-associated microbial communities in hydroponic systems, they provide an ideal design for isolating plant-microbial interactions and identifying key components possibly contributing to plant health.

Phytoremediation of methylene blue using duckweed (Lemna minor)

Azo dyes are the largest class of synthetic dyes and are utilized in several industries. Effluents containing dyes are released to the environment and pose harm to humans who might be exposed to these contaminants. This study aims to investigate the removal of methylene blue (MB) dye using duckweed (Lemna minor). L. minor (2 g) was exposed into 50 mg/L of MB dyes for 24 h. The absorbance values were measured at 0, 0.5, 1, 2, 3, 4, 5, 6, and 24 h with a maximum wavelength of 665 nm. The dye removal percentage and relative growth rate of L. minor during exposure to MB were observed. The removal percentage was 80.56 ± 0.44% for 24 h with a relative growth rate of 0.006/h. L. minor has potential as a phytoremediation agent to remove dyes from wastewater.

Comparison of floating-bed wetland and gravel filter amended with limestone and sawdust for sewage treatment

Advancements in the design and technology of constructed wetlands for efficient removal of wastewater contaminants are ever in progress to develop situation-based economical systems. Here, we entrenched two horizontal sub-surface flow constructed wetlands (HSFCW) with either chemical, viz. limestone (HSFCW-LS) or organic, viz. sawdust (HSFCW-SD) substrates, and compared them with biological method, viz. growing of water spinach in floating-bed-constructed wetland (FBCW-WS) to enhance the performance of CWs. Same sewage wastewater was used as influent in each fortified CW replicated thrice. Sewage was replaced weekly, for a total of 12 weeks of experimentation. Sampling of raw sewage from influent was undertaken at the inlet in the beginning, and that of treated effluent from the outlet after a week of treatments. Quality of raw sewage used weekly during experimentation remained almost uniform and near to the wastewater standards. Cumulative data of treated wastewater depicted that the FBCW-WS achieved the highest performance in the removal of total nitrogen (TN), [Formula: see text]-N, and total phosphorus (TP) with average removal efficiencies of 75.9, 90.5, and 94.3%, respectively. Whereas, HSFCW-SD performed better for [Formula: see text]-N, FC, and TSS with corresponding removal efficiency of 77.5, 64.3, and 74.2% while HSFCW-LS showed average performance. This study concludes that performance of biological method of macrophyte cultivation (FBCW-WS) is significantly superior to chemical and organic substrates, so it could be more effective, economical, and sustainable approach for sewage treatment.

Study on the purification effect of aeration-enhanced horizontal subsurface-flow constructed wetland on polluted urban river water

The issue of urban river pollution has attracted great attention due to high concentrations of ammonia nitrogen (NH₄⁺-N) and low concentrations of dissolved oxygen (DO) in polluted water bodies. In order to investigate the effects of aeration-enhanced horizontal subsurface-flow constructed wetlands on polluted river water, unaerated aeration (NA), continuous aeration (CA), and intermittent aeration (IA) constructed wetlands were established. The purification effects of the wetland on various pollutants and the form of effluent nitrogen, influences of temperature on the removal rates of pollutants, the change of redox potential-oxidation reduction potential (ORP)-and the difference of dissolved oxygen (DO) between influent and effluent were investigated. The results indicated that aeration enhancement can improve the purification efficiencies of chemical oxygen demand (COD) and NH₄⁺-N in constructed wetlands. The purification efficiencies of TN in IA and CA constructed wetlands were 91.9% and 53.7%, respectively, indicating that IA is the optimized aeration method for removal of various pollutants in wetlands. Changes of DO and ORP in effluent under IA and CA suggested improvement of aeration on the water environment. Meanwhile, DO was more sensitive to temperature compared with ORP. Additionally, a study of the nitrogen content in effluent suggested that the aeration method had a significant influence on the nitrogen content in effluent. The removal rates of both NH₄⁺-N and TN degraded as the temperature dropped. The results also demonstrated that the removal rate of NH₄⁺-N under aeration condition was more sensitive to temperature than that under NA condition and the effect of temperature on the removal rate of NH₄⁺-N was greater than that of TN.

The effect of inorganic salt in wastewater on the viscosity of coal water slurry

The preparation of coal water slurry (CWS) using wastewater, which contains inorganic and organic components, is one method of wastewater utilization. In this study, the effect of inorganic salts on the viscosity of CWS was examined. The results show that monovalent salts (NaCl, KCl) decreased the viscosity of CWS. The viscosity of CWS was not affected by bivalent salts (CaCl₂, MgCl₂). However, CWS combined with trivalent salt (AlCl₃) sharply increased the viscosity. The zeta potential of CWS with inorganic salts increased which can enhance the electric repulsion and beneficial to reduce the viscosity. The content of free water in CWS with trivalent salt decreased, and the freedom of the free water in CWS with trivalent salt decreased which were all bad to the viscosity and the adsorption of the dispersant on the particles. Compared with the surface polarity of the particles without inorganic salts, the surface polarity of the particles with divalent salts was similar to those without inorganic salts. Under the comprehensive influence, divalent salt has little effect on the viscosity of CWS.

Constructed wetland microcosms as sustainable technology for domestic wastewater treatment: an overview

Constructed wetland microcosms (CWMs) are artificially designed ecosystem which utilizes both complex and ordinary interactions between supporting media, macrophytes, and microorganisms to treat almost all types of wastewater. CWMs are considered as green and sustainable techniques which require lower energy input, less operational and maintenance cost and provide critical ecological benefits such as wildlife habitat, aquaculture, groundwater recharge, flood control, recreational uses, and add aesthetic value. They are good alternatives to conventional treatment systems particularly for smaller communities as well as distant and decentralized locations. The pH, dissolved oxygen (DO), and temperature are the key controlling factors while several other parameters such as hydraulic loading rates (HLR), hydraulic retention time (HRT), diversity of macrophytes, supporting media, and water depth are critical to achieving better performance. From the literature survey, it is evaluated that the removal performance of CWMs can be improved significantly through recirculation of effluent and artificial aeration (intermittent). This review paper presents an assessment of CWMs as a sustainable option for treatment of wastewater nutrients, organics, and heavy metals from domestic wastewater. Initially, a concise note on the CWMs and their components are presented, followed by a description of treatment mechanisms, major constituents involved in the treatment process, and overall efficiency. Finally, the effects of ecological factors and challenges for their long-term operations are highlighted.

Use of broken brick to enhance the removal of nutrients in subsurface flow constructed wetlands receiving hospital wastewater

Eight horizontal subsurface flow pilot scale artificial wetlands were constructed to evaluate the effectiveness of broken brick to remove nutrients from hospital wastewater. The average total suspended solids (TSS), 5-day biochemical oxygen demand (BOD5), chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN), NH4-N, NO₃-N, and phosphate percent removal efficiency of constructed wetlands were, respectively, 93.2%, 90.4%, 83.7%, 64%, 64.3%, 52.1% and 56.1% in the dry season and 89.7%, 85.8%, 82.9%, 66%, 62.7%, 56.1% and 59.5% in the rainy season. Broken brick bed wetlands provide better removal efficiency of TKN, ammonia, nitrate, and phosphate with an average removal rate of 73%, 71.3%, 79.6% and 77.1% in the dry season and 74.7%, 70.7%, 70.9% and 73.6% in the rainy season, respectively, and it provides better adsorption sites for ammonium, nitrate, and phosphate. Typha with the broken brick bed significantly improved (P < 0.05) the treatment performance of the constructed wetland systems for the removal of ammonia, nitrate, and phosphate. The seasonal variation could not significantly influence the removal of all the pollutants, but better performance of nitrate and phosphate was achieved in a dry season. Use of locally available broken brick as a substrate media can increase the nutrient removal efficiency of wetlands at a cheaper cost when applied in full scale constructed wetlands.