Bacterial community dynamics in a Myriophyllum elatinoides purification system for swine wastewater in sediments

doi:10.1016/j.apsoil.2017.05.019

Applied Soil Ecology

Volume 119, October 2017, Pages 56-63

https://doi.org/10.1016/j.apsoil.2017.05.019 Get rights and content

Highlights

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Higher diversity of bacteria was found in high concentration swine wastewater.
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Bacterial diversity was strongly positive correlation with DO.
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Bacterial community distribution was strongly positive correlations with N and P.
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Proteobacteria played an indispensable roles in M. elatinoides purification system.
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Bacterial community dynamics was responsive to swine wastewater treating process.

Abstract

Constructed wetlands are important ecological tools for treating municipal, industrial, and agricultural wastewater. Terminal restriction fragment length polymorphisms and clone libraries were employed to determine the variation in bacterial community diversity and structure from a Myriophyllum elatinoides purification system used to treat different concentrations of swine wastewater. Experiments included tap water (control), a low concentration of swine wastewater (S1, 200 ppm NH₄⁺), and a high concentration of swine wastewater (S2, 400 ppm NH₄⁺) in small tanks. The total nitrogen (TN) and total phosphorus (TP) removal efficiency were equal to or greater than 93.9% and 93.1%, respectively, in 28 d. Higher diversity of bacteria was found in S2 on day 7 and day 14. In total, 221 genera representing 17 phyla were detected. Acidobacteria and Proteobacteria dominated at the phylum level in sediments, with relative abundance ranging from 33.3% to 50% and 26.2 to 42.9%, respectively. Proteobacteria was primarily represented by Betaproteobacteria and Deltaproteobacteria at the class level on days 7, 14, and 28, and Nitrospira was detected on day 7. Verrucomicrobia was positively related to NH₄⁺ (Pearson’s correlation, P < 0.05), Bacteroidetes was negatively related to NH₄⁺ (P < 0.05). Redundancy analysis revealed that the bacterial community distribution was strongly positively correlated with TN, ammonia, TP, and phosphate in S1 and S2, these environmental parameters had a much stronger effect on S2 than S1. However, the bacterial diversity was strongly positively correlated with dissolved oxygen (P < 0.01). Certain bacteria were implicated in nitrogen and phosphorus removal in the M. elatinoides purification system, and the bacterial community dynamics changed as the environmental factors were altered during purification, therefore, wastewater parameters could predict the microbial community structure. Our results reveal microbial N and P removal process, which are important for M. elatinoides purification system studies in the field.

Introduction

Constructed wetlands (CWs) are often used for purifying wastewater from municipalities, agriculture, and industry (Dong and Reddy, 2010, Zhong et al., 2011). Although studies on types of plants, hydraulic retention time, and substrate for CWs have improved wastewater treatment (Ballantine and Schneider, 2009, Borin and Salvato, 2012), studies of microbial community structure during treatment are limited (Faulwetter et al., 2009).

Microbes play an importance part in nitrogen (N) removal and cycling in CWs (Wan et al., 2011). Various types of microbes might affect the pollutant removal efficiency and have different contributions to wastewater treatment in CWs (Ibekwe et al., 2003). During wastewater treatment, N was primarily removed by microbes involved in nitrification and denitrification (Truu et al., 2009). Furthermore, Wang and Gu (2013) suggested that microbial diversity and abundance are improved by plants in CWs. Roots may be the most important part of the interaction between plants and microbes (Gagnon et al., 2007). Microbial community dynamics will provide valuable insights into the pollutant removal process of CWs.

Ibekwe et al. (2016) reported that different bacterial communities responded to the composition of different nutrients and the decomposition process in CWs that treat swine wastewater. However, CWs are still not efficient at removing high N from swine wastewater. Much of this is attributable to plants, which commonly cannot tolerate the high N concentration in swine wastewater in CWs (Reddy et al., 2001). To treat swine wastewater effectively with CWs, the right plant species must be carefully chosen to increase N removal efficiency. A perennial floating plant, Myriophyllum elatinoides Gaudich, can grow in N-rich and P-rich environments and dramatically decrease N and P in wastewaters (Liu et al., 2013). However, little is known about bacterial community dynamics in swine wastewater purification systems treated with M. elatinoides.

The aim of this study was to analyze the diversity and composition of the bacterial community in a M. elatinoides purification system using terminal restriction length polymorphisms (T-RFLP) and clone libraries in a small-scale experiment. Bacterial community dynamics will provide us with a better understanding of microbial removal N and P processes, which could confirm the relationship between the N, P removal process and microbial community structure, potentially enabling control of bacterial communities in the M. elatinoides purification system in the field.

Section snippets

Experimental design

Wetland cells were established with plastic rectangular tanks of 0.5 m (length) by 0.4 m (width) by 0.5 m (depth). Each wetland cell was planted with one hundred M. elatinoides shoots and filled with air-dried paddy soil, and ultisol. Plants were cultivated in tap water for five days. Then the tanks were completely drained, and 15 L of wastewater was added to each wetland cell. The experiment included a control (CK, tap water), swine wastewater diluted with tap water at a 1:1 (v/v) ratio (S1,

Wastewater physicochemistry

In the M. elatinoides purification system for treating different concentrations of swine wastewater, the following characteristics were analyzed: NH₄⁺, NO₃⁻, TN, TP, PO₄³⁻, and DO (Table 1). There are significant difference in NH₄⁺, TN, TP, PO₄³⁻, and DO between different treatments from day 0 to day 28. On day 7 and day 14, NH₄⁺, TN, TP and PO₄³⁻ concentration decreased quickly, and DO concentration appear to show a rising trend in S1 and S2. However, in S1 and S2, the NO₃⁻ increased greatly

Treatment efficiency of the M. elatinoides purification system

The concentrations of TP, and PO₄³⁻ declined to 6% of the original concentration from day 0 to day 28 in the M. elatinoides purification system (Fig. 1). The removal efficiency of P in this system is much higher than previously reported (Dong and Reddy, 2012, Ibekwe et al., 2016). Our N and DO results are also discussed in a previous study (Li et al., 2015). These results indicate that the M. elatinoides purification system could be used for treating swine wastewater in the field.

Bacterial diversity and composition in the M. elatinoides purification system

In this study,

Conclusions

In this study, bacterial community dynamics of a M. elatinoides purification system treating different concentrations of swine wastewater were investigated using clone libraries. Wastewater parameters such as TN, NH₄⁺, TP, and PO₄³⁻ decreased markedly in the M. elatinoides purification system. There were differences in bacterial diversity and composition in sediments from different concentrations of swine wastewater. The results showed that undiluted swine wastewater supported more diversity

Acknowledgments

This study was financially supported by the Open Foundation of Key Laboratory of Agro-ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, the Chinese Academy of Sciences (ISA2015302), the National Science and Technology Supporting Project (2014BAD14B00), and Ministry of Water Resources Public Service Industry, a Special Fund (201501055). We thank Public Service Technology Center, Institute of Subtropical Agriculture, the Chinese Academy of Sciences for providing

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