Can wetlands reduce humic substances in forested streams : combining two approaches to characterize efficiency

Establishing statistical significance in assessing wetland performance can be quite challenging when reduction in the monitored substance is very small and temporarily variable. Assessing colour changes associated with humic substances is such a situation. One of the most important parameters of any evaluation of wetland treatment performances is the retention time of the water before it exit the wetland. This can be theoretically estimated, but even better measured directly with the help of a tracing agent. In this research, the approach is based on the simultaneously assessment of hydraulic retention time using conservative tracing (Rhodamine WT) and a mass balance based removal efficiency assessment (regression slope of the summation mass-in vs. summation mass-out)

Low cost rainwater harvesting : an alternate solution to salinity affected coastal region of Bangladesh

This study investigated the prospect of rainwater harvesting as a low cost alternative potable water supply option along the coastal region of Bangladesh, which is considered as one of the most vulnerable countries in the world due to climate change and resulting sea level rise. Because of increasing salinity intrusion, potable water scarcity become severe at the south-western coastal region of the country. The study area for this investigation was Patkelghata in Satkhira district of Bangladesh located in the same zone. The Satkhira district averages nearly 1,710 mm rainfall per year. Based on rural housing pattern of the region, a rainwater harvesting system is proposed, which consists of roof catchment, gutters, down pipes, first flush devices, filter chamber and storage tank. The minimum catchment area was assumed to be 6 m2 and storage tank of 2000 liter capacity. Data was collected on the present state of freshwater supply, sources and quality, average rainfall in the region, dry spell period, family size, water use nature, rain water quality and material to be used for storage, etc. Rainwater quality was also tested and the parameters were found to be within Bangladesh’s standard limit. After a detail calculation, an approximate cost was assumed to be $171 for building and operation of the whole system. A questionnaire survey was also conducted on views and opinion of local people to understand the problems, prospects and the popularity of rainwater harvesting in Bangladesh

Capacity of Vitiver grass in treatment of a mixture of labaratory and domestic wastewaters

 In this study, laboratory wastewater containing organic matters, heavy metals and aromatic compounds, was treated by vetiver grass (Vetiveria zizanioides) as a phytoremediation method to remove the above three groups of pollutants. Sewage effluent, as a source of nutrient supply for plant growth, was firstly fed to two wetland systems: mini horizontal subsurface flow (HSSF) and floating raft (FR) wetlands. Next, laboratory wastewater was added gradually to mix with sewage. Nominal hydraulic retention time in both wetlands are 12 hours. Pollutants removal efficiencies were monitored. Microbial community change corresponding with each stages of sewage only and mixture with laboratory wastewater was also examined. The examined microbial community includes Nitrogen-fixing (N-fixing) bacteria, Phosphate-solubilizing (P-solubilizing) microorganism, Pseudomonas sp., and Zoogloea sp.  In HSSF wetland, base materials (gravel and sand), algae, and vetiver root were in turn investigated for pollutant removal efficiencies. The results reveal that even with the presences of heavy metals and aromatic compounds, vetiver presented reasonable removal efficiencies of about 62%, 68.6%, and 58.3% for BOD, TN, and TP removal, respectively. Base materials showed almost no effect on pollutant removal. Algae was slightly responsible for approximate 6.3%, 16.6%, and 19.7% of BOD, TN, and TP removals, respectively. On the other hand vetiver roots, in term of heavy metals, had an impressive removal efficiencies of 99.2, 95.8, 96.2, and 96.7% of Cr+6 (in K2Cr2O7), Mn (MnSO4), Fe (FeSO4), and Cu (CuSO4), respectively. For aromatic compounds, the wetland is responsible for 96.8 and almost 100% of correspondingly phenol and benzene removal efficiencies. For microbial aspect, N-fixing microorganisms (e.g. Azospirillum sp., Azotobacter sp.) and Phosphate-solubilizing bacteria (Bacillus sp.) increased gradually in population during domestic wastewater feeding stage. When laboratory wastewater was added, N-fixing and P-solubilizing bacteria were quantitatively decreased slightly while population of Pseudomonas sp. increased. Besides, Zoogloea sp. was also found increasing through out the experiment and keeping a stable growth even during laboratory wastewater adding.  In FR wetland, both algae and vetiver root were also investigated for BOD and aromatic compounds and heavy metals. The outcomes show similar tendencies in treatment and microbial behaviours as in HSSF wetland. Vetiver grass, mainly responsible for organic matters and nutrients removal, presented slightly lower removal efficiencies than those in HSSF wetland. The average values of removal efficiencies are 59%, 63.5%, and 53.0% for BOD, TN, and TP removal, respectively. Algae, also, took minor responsibility for approximate 3.3%, 9.1%, and 8.9% of BOD, TN, and TP removals, respectively. Heavy metals of Cr+6 (in K2Cr2O7), Mn (MnSO4), Fe (FeSO4), and Cu (CuSO4) were found removing less than in HSSF wetland with average removal efficiencies values of 92.4, 85.1, 91.8, and 91.5%, respectively, by  vetiver root. Algae show almost no effect on heavy metals and aromatic removals. The vetiver root likewise plays important role in phenol and benzene removals with values of 91.5 and 96% in efficiency, respectively. N-fixing and P-solubilizing microorganisms, Pseudomonas sp., and Zoogloea sp. presented similar responses tendencies to different living condition when domestic and laboratory wastewaters, in turn, were fed