Use of ecological concrete for nutrient removal in coastal sediment and its effects on sediment microbial communities

A critical review of the mechanisms, factors, and performance of pervious concrete to remove contaminants from stormwater runoff

Stormwater can carry pollutants accumulated on impervious surfaces in urban areas into natural water bodies in absence of stormwater quality improvement devices. Pervious concrete (PC) pavement is one of the low-impact development practices introduced for urban flooding prevention and stormwater pollution reduction. PC removes various types of water contaminants. Mechanisms contributing to the water pollution removal capacity of PC can be categorized into three groups: physical, chemical, and biological. Properties of PC such as permeability, porosity, thickness, and adsorption capacity influence removal of all contaminants, although their impact might differ depending on the pollutant properties. Chemical mechanisms include precipitation, co-precipitation, ion and ligand exchange, complexation, diffusion, and sorption. Bulk organics and nutrients are removed primarily by biodegradation. Physical filtration is the primary mechanism to retain suspended solids, although biological activities may have a minor contribution. Release of calcium (Ca2+) and hydroxide (OH-) from hardened cement elevates the effluent pH, which is an environmental concern. However, the pH elevation is also the prime contributor to heavy metals and nutrients removal through precipitation. Specific cementitious materials (e.g., Pozzolans and nanoparticles) and carbonation curing approach are recommended to control effluent pH elevation. Complexation, diffusion, ion solubility, and stability constants are other mechanisms and parameters that influence heavy metal removal. Organic matter availability, electrostatic attraction, temperature, pH, contact time, specific surface area, and roughness of PC pores contribute to the pathogen removal process. Although PC has been found promising in removing various water pollutants, limited salinity removal can be achieved due to the inherent release of Ca2+and OH- from PC.

Mesocosm experimental study on sustainable riparian restoration using sediment-modified planting eco-concrete

The continued deterioration of riparian ecosystems is a worldwide concern, which can lead to soil erosion, plant degradation, biodiversity loss, and water quality decline. Here, taking into account waste resource utilization and eco-environmental friendliness, the sediment-modified planting eco-concrete with both H. verticillata and T. orientalis (SEC-H&T) was prepared and explored for the first time to achieve sustainable riparian restoration. Concrete mechanical characterizations showed that the compressive strength and porosity of SEC with 30% sediment content could reach up to 15.8 MPa and 21.25%, respectively. The mechanical properties and the sediment utilization levels of SEC were appropriately balanced, and potentially toxic element leaching results verified the environmental safety of eco-concrete modified with dredged sediments. Plant physiological parameters of both aquatic plants (biomass, chlorophyll, protein and starch) were observed to reach the normal levels in SEC during the 30-day culture period, and T. orientalis seemed better adapted to SEC environment than H. verticillate. Importantly, compared to SEC-H and SEC-T, SEC-H&T could effectively reduce the concentrations of COD, TN and TP by 58.59%, 74.00% and 79.98% in water, respectively. Notably, water purification mechanisms by SEC-H&T were further elucidated from the perspective of microbial community responses. Shannon index of bacterial diversity and proliferation of specific populations dominating nutrient transformation (such as Bacillus and Nitrospira) was increased under the synergy of SEC and aquatic plants. Correspondingly, functional genes involved in nitrogen and phosphorus transformation (such as nosZ and phoU) were also enriched. Our study can not only showcase an effective and flexible approach to recycle dredged sediments into eco-concrete with low environment impacts, but also provide a promising alternative for sustainable riparian restoration.

Response of microbial communities to nutrient removal in coastal sediment by using ecological concrete

Ecological concrete (eco-concrete) is a kind of environment-friendly material with porous characteristics. In this study, the eco-concrete was used to remove the total nitrogen (TN), total phosphorus (TP), and total organic carbon (TOC) in marine coastal sediment. The bacterial communities in sediment and on eco-concrete surface were also investigated by using high-throughput sequencing and quantitative PCR of 16S rRNA gene. We found that the mean removal efficiencies of TN, TP, and TOC in treatment group were 8.3%, 8.4%, and 12.3% after 28 days. The bacterial community composition in the treatment group was significantly different from that in the control group on day 28. In addition, the bacterial community composition on eco-concrete surface was slightly different from that in sediment, and the copy numbers of 16S rRNA gene were higher on eco-concrete surface than in sediment. The types of eco-concrete aggregates (gravel, pebble, and zeolite) also had effects on the bacterial community composition and 16S rRNA gene copy numbers. Furthermore, we found the abundant genus Sulfurovum increased significantly on eco-concrete surface in the treatment group after 28 days. Bacteria belonging to this genus were found having denitrification ability and were commonly detected in bioreactors for nitrate removal. Overall, our study expands the application scopes of eco-concrete and suggests that the bacterial communities in eco-concrete can potentially enhance the removal efficiency of nutrients in coastal sediment.

Treatment of Wastewater Effluent with Heavy Metal Pollution Using a Nano Ecological Recycled Concrete

Water pollution exacerbates water stress and poses a great threat to the ecosystem and human health. Construction and demolition waste (CDW) due to rapid urbanization also causes heavy environmental burdens. A major proportion of CDW can be effectively converted into recycled aggregates, which can be reused in many fields, including environment remediation. In this study, a nano ecological recycled concrete (nano-ERC) was produced with recycled aggregates and copper oxide nanoparticles (nCuO) to remove heavy metals (HMs) from a simulated wastewater effluent (SWE) for further treatment. Recycled aggregates were obtained from CDW, thereby simultaneously reducing the treatment cost of the SWE and the environmental burden of solid waste. The adsorption capacity of nano-ERC was presumed to be significantly enhanced by the addition of nCuO due to the unique large surface-to-volume ratio and other properties of NPs. The SWE containing five common HMs, arsenic (As), chromium (Cr), cadmium (Cd), manganese (Mn) and lead (Pb), was filtered through a control ERC and nano-ERCs, and the concentrations of these HMs were determined with ICP-MS in the SWE and the filtrates. Results showed the nano-ERCs could significantly remove these HMs from the SWE compared to the control ERC, due to the enhanced adsorption capacity by nCuO. The relative weighted average removal percentage (RWAR%) was in the range of 53.05–71.83% for nano-ERCs and 39.27–61.65% for control ERC. Except for Cr, concentrations of these HMs in the treated wastewater effluent met the requirements for crop irrigation or scenic water supplementation; the Cr may be removed by multiple filtrations. In conclusion, nano-ERC can serve as a cost-effective approach for the further treatment of wastewater effluent and may be applied more widely in wastewater treatment to help relieve water stress.

Treatment of dairy wastewater by immobilized microbial technology using polyurethane foam as carrier

The development of dairy industry is accompanied by large volumes of wastewater production, which is threaten to human's health and the biosphere. In this study, synthetic dairy wastewater was treated by immobilized microbial technology using polyurethane foam as carrier. Batch experiments were conducted to determine the effects of different operational parameters, and an up-flow immobilized microbial reactor was built to investigate long-term performance of the system. Batch experiments showed that COD, TN and NH₃-N dropped from 1932, 51.33 and 51.42 mg·L^-1 to 75.3, 5.17 and 4.54 mg·L^-1 after 48 h, respectively, at the optimum conditions (25 °C, pH 6.0). Besides, the reactor can remove 97.33% of COD, 96.46% of TN and 99.55% of NH₃-N with HRT of 24 h, which the average volume load was 1.93 kg COD·(m³·d)^-1. The analysis of microbial community determined that dominant bacteria at genus level were Acinetobacter, Fusibacter, Nannocystis and norank _f_NS9_marine_group.

Investigating Planting Concrete Suitability by Evaluating the Physiological Indexes of Three Ground Cover Plants

Concrete is one of the most widely used construction materials for basic infrastructure worldwide, especially in developing areas undergoing rapid urbanization. However, concrete inhibits energy exchange between soil and other ecosystem components. To enhance the fluxion of information between ecosystems, surface vegetation, and basement soil, this paper aims to explore the tolerance of plants growing on PC. Therefore, we investigated two different PC sample groups with aggregate particle diameters of 5–10 and 15–20 mm. After curing, the samples were used to plant three ground cover plants (Cynodon dactylon(L.) Pers, Agrostis stolonifera, and Sasa argenteostriatus, e.g., Camus), and the results were compared with those from normal soil without PC underneath as a reference. During an observational period of 12 weeks, the growth and height of the plants were documented and analysed. The physiological indexes of free proline (Pro), malondialdehyde (MDA), chlorophyll (Chl), relative electrical conductivity (REC), and soluble protein (SP) were investigated. The correlations and significant differences between these indexes based on the treatments were analysed. Then, principal component analysis (PCA) was used to determine the main variables affecting plant growth. The results showed that there were significant differences between the PC groups and the natural growth group. The growth and height of the three plant species under near-natural (nonconcrete) conditions were better than those of the plants in the PC treatments. The plants in the large-particle concrete (LC) treatment group showed better adaptability than those in the small-particle concrete (SC) treatment group in terms of growth, although both PC treatments resulted in various degrees of damage. PCA showed that SP, REC, and MDA were the most influential factors on plant growth in this study.

Transformations from specialists to generalists cause bacterial communities are more stable than micro-eukaryotic communities under anthropogenic activity disturbance

Different microbial components have different responses to environmental disturbances. Here, we found that the planktonic bacterial and micro-eukaryotic communities had different responses to anthropogenic activity disturbance in a subtropical river, because they had different survival strategies (generalist and specialist). We used nutrients (nitrogen and phosphorus) as indicators of anthropogenic activities. We found that river stretch 1 showed low nutrient concentrations from October 2018 to September 2019. However, a nutrient disturbance was observed in river stretch 2. The nutrient concentrations increased largely in December and January but recovered to low values in June. Bacterial communities had higher resilience under this disturbance than micro-eukaryotic communities in river stretch 2. The bacterial community composition were quite different between the two river stretches in December and January but were similar in June and July. However, the differences of micro-eukaryotic community composition between the two river stretches were always high during the study period. The bacterial communities in river stretch 2 contained more generalists and nutrient tolerant specialists. The bacterial nutrient tolerant specialists rapidly decreased in the low nutrient months and were replaced by the generalists. Bacteria which were involved in this shifts accounted for 29.3% of the total abundance. However, the micro-eukaryotic communities in river stretch 2 contained more moderate generalists. These moderate generalists were insensitive to the variation of nutrients and only 19.56% of the micro-eukaryotes had significant responses to the disturbance. The survival strategies caused bacterial communities had higher adaptability than eukaryotes to environmental fluctuation.