Phosphorus bioavailability and the diversity of microbial community in sediment in response to modified calcium peroxide ceramsite capping
Graphical abstract
Introduction
Capping inactive material to control phosphorus (P) in water-sediment interface has been used widely as a restoration method in eutrophic lakes, such as Phoslock®. However, the physical barrier is generated at sediment-water interface when capping with materials, which induces the anaerobic environment inside the sediment. The bioavailable P (BAP) concentration would be redistributed towards an adverse direction and the growth of microorganisms in anaerobic sediment resists the removal of P. This effective P removal method is at the expense of the sediment which is temporary, hence, the restoration of sediment should be encouraged (Horppila et al., 2019).
The BAP is a vital element to value the potential of P release in sediments, which is comprised of water-soluble P (WSP), algal available P (AAP), readily desorbable P (RDP) and Olsen-P (Li et al., 2011). BAP is regarded as the mainly dissolved orthophosphate which is immediately available for algal growth (Pan et al., 2012; Soliman et al., 2017). The external P input or the internal P release from sediment directly affects the distribution of BAP in the sediments. The concentration of BAP depends on the reactions of adsorption-desorption, precipitation-dissolution and reduction-oxidation, which also impact the content of dissolved P that released from sediments (Mbabazi et al., 2019). Therefore, the control on BAP plays an important role during the inhibition of internal P release.
In the case of co-precipitation of P with metal compounds such as calcium carbonate, crystalline iron oxides or association with more resistant forms of organic matter, its bioavailability will almost trend to decrease. Lin et al. (2019) found that lanthanum compounds had a higher BAP immobilization capacity. Wang et al. (2017) reported that drinking water treatment (DWTR) and Phoslock® could increase the removal of BAP from 34% to 63% and 63%–69%, respectively. Xu et al. (2018) investigated that pure CaO2 under the point injection could result in the sharp reduction of BAP in the sediment. However, the applications of CaO2 to control BAP are limited. The main reason is the quick reaction speed between CaO2 and water, resulting in the dosage of CaO2 exceeding the demand, and the inhibition on the bacterial in the sediments, smothering the restoration of eutrophic water bodies.
There is an increasing trend on research of modification methods based on CaO2 to retard oxygen supply by decreasing the reaction speed. Lee et al. (2014) prepared oxygen-releasing alginate beads by adding and mixing CaO2 to the solution of sodium alginate in water for bioremediation of contaminated groundwater, extended the oxygen supply period to seven days. In previous study (Zhou et al., 2018), the modified calcium peroxide ceramsite (MCPC) made by bonding calcium peroxide, cement and water purification sludge at a suitable ratio. MCPC not only had a better P adsorption capacity, but also could retard the reaction rate of CaO2 to hinder the oxygen release. Additionally, modified CaO2 can supply hydroxyl radical (·OH), which is a strong oxidation material. This is hypothesized to inhibit the sedimentary P release. Li et al. (2010) found that sediment re-suspension reduced the concentration of BAP, which attribute to the strong oxidation and the precipitation between P and metal ions. However, it has seldom been applied or tested for the modified CaO2 material (MCPC) to control BAP. This study is based on the hypothesis that MCPC could change BAP in the sediments due to its supply with Ca2+ and oxygen.
Generally, CaO2 can significantly promote microbial growth in the soil due to the supply of oxygen. Wang et al. (2019a, 2019b) found that CaO2 redistributed the structure of microbial community by decreasing the abundance of anaerobic bacteria meanwhile increasing the aerobic bacteria with some functional bacteria. Zhang et al. (2016) reported that the new porous ceramic filter media increased the relative abundance of Firmicutes and Nitrospirae at the phylum level which enhanced the function of P metabolism. The P metabolism could promote the transformation of P from bioavailable fractions to nonbioavailable fractions which induced the P disappearance. It is suggesting that the microorganisms in the sediments depends on the capping materials.
Teng et al. (2018) reported that the microbial community structure has a significant impact on P interception and its characteristics tend to be closely related to the concentration of BAP. Bokhorst et al. (2017) discovered that the increase of BAP was attributed to the changes in microbial activity and sediment physicochemical characteristics. It is speculated that CaO2 can not only change BAP but also the microbial community, but the relationship between BAP and microbial community under the capping with modified CaO2 material still remains poorly understood.
This study is focusing on investigation of the effect of MCPC on BAP and microbial community in sediment. MCPC was applied in the experiment under the external P input for a long term to assess: (1) the variations of BAP in sediment; (2) the change of microbial community in sediment; (3) the relationship between BAP and microbial community due to the change of the micro-environment. The aim is to clarify the mechanism of BAP inhibition under the capping with MCPC.
Section snippets
Materials
Modified calcium peroxide ceramsite (MCPC) were prepared by calcium peroxide, cement and water purification sludge at the ratio of 5:2:3. Detailed physical and chemical properties about MCPC are described in Zhou et al. (2019).
Site description and sample collection
The overlying water and sediment were sampled from the canal in Suzhou City of China (N31°16′23.86″, E120°37′50.43″; depth: 2–3 m), recognized as a representative eutrophic canal which receives the sewage discharge from nearby residential buildings.
A piston corer sampler
P adsorption and release performance under MCPC capping
To investigate P adsorption and release performance under MCPC capping, the external P was added until the P adsorption of MCPC reaching saturation. During the experiment, the variation of DIP concentration was monitored, and then the amount of P disappearance and release was calculated at the end of the experiment. As shown in Fig. 1, under MCPC capping, a large disappearance of P from overlying water and a slight release of P from sediments were observed compared with the control. The
Conclusions
Under capping with MCPC, the obvious P disappearance was observed and the P release potential was reduced as the result of the strong adsorption capacity of MCPC. The concentrations of NH4+-N and Fe(Ⅱ) in the pore water decreased significantly and kept at low levels compared with the control. It is showing that MCPC induced the transformation of microenvironment in the sediment from anaerobic conditions to aerobic conditions, which result in the reduction of BAP in the sediments compared with
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This study was supported by the National Natural Science Foundation of China (grant Nos. 51778393), Collaborative Innovation Center of Water Treatment Technology and Material of Jiangsu Province of China, National and Local Joint Engineering Laboratory of Municipal Sewage Resource Utilization Technology of China.
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