Impacts of sanitation improvement on reduction of nitrogen discharges entering the environment from human excreta in China

Constructed wetlands as hotspots of antibiotic resistance genes and pathogens: Evidence from metagenomic analysis in Chinese rural areas

In rural China, many constructed wetlands (CWs) have been developed to treat rural wastewater sustainably. However, due to the scarce information on those rural CWs, it is difficult to analyze the biological contaminants within those systems, such as antibiotic resistance genes (ARGs) and pathogens. Based on the data collected from two pilot-scale, one-year-observed CWs, for the first time, this study explored the accumulation of ARGs and pathogens using the metagenomic sequencing approach and SourceTracker analysis under different hydraulic loading rates. The Shannon index of ARGs in the effluent surpassed the level found in the influent. The DESeq2 analysis showed that up to 21.49% of the total pathogen species had increased relative abundance in the effluent compared with the influent. By combining the contribution of substrate and rhizosphere, the CW became a more influencing factor for ARGs and pathogens contamination than the influent. The network analysis revealed a critical but latent fact that the development of antibiotic-resistant pathogens is highly likely to be triggered by the co-occurrence of ARGs and pathogens. Collectively, from the aspect of biological risk, our study showed that CWs alone might not be an ideal solution for improving wastewater treatment in rural China.

Potential barriers in implementing the rural toilet retrofitting project: A qualitative study in Jiaozuo, China

Background

China has launched a large "toilet revolution" in rural areas, but the results show that sanitation has not always been markedly improved. Few scholars have paid attention to this issue, and the list of the reasons is scattered and incomplete.

Method

Using the qualitative research method, this study interviewed seven village cadres and 39 villagers in three villages of Jiaozuo City to examine the implementation barriers to rural toilet retrofitting (RTR) projects in China.

Results

Using the Van Meter and Van Horn policy implementation approach, the research has found that: (a) unreasonable standards and objectives fail to incorporate local conditions and improve the actual quality; (b) lack of capital and human resources cannot renovate new toilets; (c) uncoordinated inter-organizational communication and enforcement activities by top-down mechanism lead to policy implementers and target groups' dissatisfaction with the policy; (d) weak and unenthusiastic, inadequate implementing agencies, reduce their working ability; (e) inappropriate economic, social and political conditions impede the villagers' acceptance; and (f) an attitude of passive acceptance by the implementers reduce the working motivation.

Conclusion

To improve sanitation in rural China, it is necessary to solve the six barriers. The findings of this study can provide recommendations and guidance for implementing the RTR and related public health policies.

Enhanced Nutrient Removal in A2N Effluent by Reclaimed Biochar Adsorption

The excessive nitrogen and phosphorus discharged into the water environment will cause water eutrophication and thus disrupt the water ecosystem and even exert biological toxicities. In this study, the absorption removal of nitrogen and phosphorus from the anaerobic tank in an anaerobic−anoxic/nitrifying system using four different kinds of biowaste-reclaimed biochars were investigated and compared. The effects of temperature and pH on nutrient adsorption removal were further investigated. The four kinds of biochar were successfully prepared and well characterized using a scanning electron microscope, fourier transform infrared spectroscopy, X-ray diffraction and Brunner−Emmet−Teller methods. Generally, there was no significant change in chemical oxygen demand (COD) and NH4+-N removal efficiencies when treated by the different biochars, while the activated sludge biochar (ASB) displayed the highest total phosphorus (TP) removal efficiency. The initial TP concentrations (<40 mg/L) displayed no remarkable effects on the TP adsorption removal, while the increase of temperature generally enhanced TP and NH4+-N adsorptions on the ASB. Besides, the increase of pH significantly promoted NH4+-N removal but depressed TP removal. Moreover, the adsorption process of TP by the ASB complies with the secondary kinetic model, suggesting the chemical precipitation and physical electrostatic interaction mechanisms of TP adsorption removal. However, the adsorption of NH4+-N conformed to the inner-particle diffusion model, indicating that the NH4+-N adsorption was mainly involved with pore diffusions in the particles.

Pilot-scale two-stage constructed wetlands based on novel solid carbon for rural wastewater treatment in southern China: Enhanced nitrogen removal and mechanism

Constructed wetlands (CWs) have been proved to be an alternative to the treatment of various wastewater. However, there are few studies focused on the removal performance and mechanisms of pollutants in pilot-scale CWs packed with novel solid carbon. In this study, we investigated the effect of poly-3-hydroxybutyrate-co-3-hydroxyvalerate/polyacetic acid (PHBV/PLA) blends as carbon source on pollutant's transformation, microbial communities and functional genes in pilot-scale aeration-anoxic two-stage CWs for polishing rural runoff in southern China. Results showed a striking improvement of TN removal in CWs with PHBV/PLA blends (64.5%) compared to that in CWs with ceramsite (52.9%). NH₄⁺-N (61.3-64.6%), COD (40.4-53.8%) and TP (43.6-47.1%) were also removed effectively in both two CWs. In addition, the strains of Rhodocyclaceae and Bacteroidetes were the primary denitrifiers on the surface of PHBV/PLA blends. Further, the aerobic stage induced gathering of 16 S and amoA genes and the anoxic zone with PHBV/PLA blends increased the nirS genes, which fundamentally explained the better denitrification performance in CW based on PHBV/PLA blends. Consequently, this study will provide straightforward guidance for the operation of engineering CWs packed with polymers to govern the low-C/N rural wastewater.

Activated Sludge Microbial Community and Treatment Performance of Wastewater Treatment Plants in Industrial and Municipal Zones

Controlling wastewater pollution from centralized industrial zones is important for reducing overall water pollution. Microbial community structure and diversity can adversely affect wastewater treatment plant (WWTP) performance and stability. Therefore, we studied microbial structure, diversity, and metabolic functions in WWTPs that treat industrial or municipal wastewater. Sludge microbial community diversity and richness were the lowest for the industrial WWTPs, indicating that industrial influents inhibited bacterial growth. The sludge of industrial WWTP had low Nitrospira populations, indicating that influent composition affected nitrification and denitrification. The sludge of industrial WWTPs had high metabolic functions associated with xenobiotic and amino acid metabolism. Furthermore, bacterial richness was positively correlated with conventional pollutants (e.g., carbon, nitrogen, and phosphorus), but negatively correlated with total dissolved solids. This study was expected to provide a more comprehensive understanding of activated sludge microbial communities in full-scale industrial and municipal WWTPs.

Impacts of water residence time on nitrogen budget of lakes and reservoirs

As an important factor related to the self-purification capacity (e.g. denitrification, burial rate, and downstream output) in aquatic systems, water residence time (WRT) has great impacts on the nitrogen (N) dynamics and its removal process in lakes and reservoirs. In this study, we have analysed the impacts of WRT on the change rates of total nitrogen (TN) concentrations in 50 waterbodies (including 33 lakes and 17 reservoirs) in China, with different change trends (e.g. increasing trends and decreasing trends) and TN concentrations during 2012-2016. Based on the annual ecosystem-scale N mass balance, TN input and output flux in the waterbodies are estimated. The results showed that the decreases of TN concentrations usually occur in the waterbodies with the relatively high TN concentrations in 2012, and WRT has significant impacts on the TN change rates in the waterbodies. Longer WRT could slow down the TN increasing rates in the waterbodies acting as N sinks, but could accelerate the removal from the waterbodies acting as N sources. Higher water phosphorus (P) concentrations could also be beneficial for the faster N removal from the waterbodies, which is mediated via the coupled processes regulating the N transfer from water column to anoxic sediments. China has recently issued the "lake-chief" systems, addressing the specific and flexible strategies for water pollution control in different lakes. The self-purification capacity through denitrification and burial rate, which are closely related to WRT, should be taken into consideration when making specific water management plans in the future.

Human activities altered water N:P ratios in the populated regions of China

Being able to quantify nutrient stoichiometry in the waterbodies is especially important given its strong effects on a variety of ecological processes. China has made huge progress in the improvement of surface water quality, but the accompanying changes to water nutrient stoichiometry and implications are not well understood yet. Our results have shown that the water nutrient cycles have been decoupled in China's populated regions, and population density and GDP values in the same catchment are useful in explaining the variances of lake N:P stoichiometry in East China Lake Region. In other regions, water N and P tend to respond to the selected parameters in a similar way, leading to the poor prediction of N:P stoichiometry. With the progress of water management in China, a similar change of water nutrients and their stoichiometry as the developed countries is occurring, i.e., faster decrease of TP concentrations than TN, and continuing increase of N:P ratios. It is necessary for the managers to be aware of the quick and large-scale changes of nutrient stoichiometry in the water, since the ecological risk caused by the changes to the aquatic systems is still not well known.

Effect of graphene oxide on the bioactivities of nitrifying and denitrifying bacteria in aerobic granular sludge

With the widespread application of graphene oxide (GO), it would be inevitably released into wastewater treatment plants (WWTPs) and get involved in the biochemical process. So far, there are controversies on the effects of low GO concentration (0.05-0.1 g/L) on the nitrogen removal process. Therefore, this study essentially investigates any potential effects of GO on wastewater microbial communities functions. In present study, the nitrifying and denitrifying batch tests were introduced to investigate the influence of 0.06 g/L of GO on bacteria. The results showed that GO could be easily combined with the aerobic granular sludge (AGS), and NH₄⁺-N was sharply absorbed, which directly promoted the bioactivities of ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) and extracellular polymeric substances (EPS) production. The influence of GO on the denitrifying bacteria was negligible, which resulted in the stable EPS production. Furthermore, as inferred from the near maximum chemical reaction rates, there were no obvious changes on the microbial community functions during nitrogen removal process.