Abstract
For verification of spatial distribution of phosphorous retention capacity in constructed wetlands systems(CWs), two horizontal subsurface flow(HSSF) CWs and two vertical subsurface flow(VSSF) CWs, using sand as substrate and Typha latifolia as wetland plants, were constructed and put into use for synthetic wastewater treatment. Five months later, significant spatial variations of TP and inorganic phosphorus(Ca-P, Fe-P and Al-P) were observed, which were found to be greatly affected by CWs type and hydraulic loading. The results revealed that though spatial distribution of Fe-P and Al-P displayed a similar order of substrate content as "rhizosphere" > "near-rhizosphere" > "non-rhizosphere" and "inflow section" > "outflow section" regardless of types and loading, the distribution of Ca-P was positively correlated to that of Fe-P and Al-P in HSSF CWs, while negative correlation was shown in VSSF CWs. As a result, TP spatial distribution in HSSF CWs demonstrated a greater dissimilarity than that in VSSF CWs. For HSSF CWs with low hydraulic loading, the lowest TP content was found in non-rhizosphere substrate of outflow section, while the highest one was discovered in rhizonsphere substrate of inflow section. The values in 6 parts of areas ranged from 0.138 g·kg-1 to 2.710 g·kg-1, which also were from -33.5% to 1209% compared to the control value. On contrast, spatial difference of TP content in substrates of VSSF CWs was insignificant, with a variation ranging from 0.776 g·kg-1 to 1.080 g·kg-1, that was 275% to 421% higher than the control value. In addition, when hydraulic loading was increased, TP content in VSSF CWs sharply decreased, ranging from 0.210 g·kg-1 to 0.634 g·kg-1. Meanwhile, dissimilarity of TP spatial distribution in HSSF CWs was reduced, with TP content ranging from 0.258 g·kg-1 to 2.237 g·kg-1. The results suggested that P spatial distribution should be taken into account for CWs design and operation.
Highlights
As low-cost approaches, constructed wetlands(CWs) were widely used for the treatment of municipal, industrial, aquacultural and agricultural wastewater, in which phosphorus was the main pollutant that constructed wetlands aimed at removing[1,2,3,4]
It showed that vertical subsurface flow CW systems could get a higher COD removal rate than that done by horizontal subsurface flow CW systems
After 5 months of operation for synthetic wastewater treatment, significant spatial variations of TP and inorganic phosphorus(Ca-P, Fe-P and Al-P) in substrates were observed, which were greatly affected by types of CWs and hydraulic loading
Summary
As low-cost approaches, constructed wetlands(CWs) were widely used for the treatment of municipal, industrial, aquacultural and agricultural wastewater, in which phosphorus was the main pollutant that constructed wetlands aimed at removing[1,2,3,4]. As a whole system, during the treatment of wastewater the P sorption process in CWs was greatly affected by the environmental factors (e.g. pH, ORP and DO)[10,11] and the operation factors, e.g. temperature and inflow loading rate(or hydraulic retention time) [12]. Take ORP for example, it was agreed that substrate could adsorb more P under aerobic condition than did under anaerobic condition[13,14,15].On the other hand, ORP would be greatly influenced by hydraulic design(type of CWs), mode of operation, plants and seasons[14,16] All these factors would affect P-sorbing capacity directly or indirectly as well. Under anaerobic condition, hydrolytic acidification of organic matter could change the physico-chemical features of substrates, such as decrease of pH level[17], reduction of Fe(III) to Fe2+ [13], extraction and release of Fe and Al [18]- and so on
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
