Prediction of dissolved oxygen in harbours using artificial neural networks: an application to the port of Colombo

Maintenance of high dissolved oxygen (DO) level in harbours is highly important as it could give rise to catastrophic effects if it is depleted affecting day- to- day port functions such as dredging activities and other maintenance work. The depletion of DO results not only in toxic gases such as methane and hydrogen sulphide but also in accumulation of wastes. Frequent monitoring of DO is therefore imperative, but creates practical difficulties due to ship movements and other activities. Hence, prediction of DO with an empirical model using Artificial Neural Networks (ANNs) was done with success with an application to the Port of Colombo (PoC). This model aims to reduce the frequency of monitoring DO and to foresee the responses of the system due to environmental changes. The performances of ANNs were compared with Multiple Linear Regression (MLR). Monthly values of 14 water quality parameters at several depths for a particular period were collected. The values of weather parameters of rainfall and wind velocity for the corresponding period were also collected. The inputs of the best model were temperature, depth and five rainfall intensities (including rainfall values on four immediate previous days). A sensitivity analysis was carried out to assess the potentials of small changes in each input on the neural network output. MLR model with the same number of input variables indicated a low value for R after several transformations. The rainfall intensity of the 3rd previous day was the most influential variable among the ANN inputs affecting the output. In conclusion, it could be inferred that the ANN model is capable of predicting DO in PoC considerably well compared with MLR

Growth characteristics of water hyacinth: an application to bolgoda lake

Water hyacinth (Eichhornia crassipes (Mart). Solms) is considered as a serious pest in many lakes, irrigation canals, stagnant ponds, waterways and semi-wet areas in Sri Lanka. Bolgoda Lake has been severely affected by excessive growth of water hyacinth, which resulted in clogging of major waterways, adversely affecting navigation. This study was carried out to determine the growth characteristics of water hyacinth under influence of the physical and chemical factors in Bolgoda Lake. The parameters such as biomass, biomass production per day, phosphorus and nitrogen content in plant tissues and pH, temperature, salinity, phosphorus and nitrogen content in the water body were measured

Heavy metal levels of groundwater in Ratmalana-Moratuwa industrial area: a comprehensive survey carried out in 2002

Ratmalana-Moratuwa industrial area has been subject to heavy pollution from various industries for more than a decade. This area is believed to have been polluted with heavy metals that have some drastic adverse impacts on human beings. Since there has not been a comprehensive study done to get an insight into the degree of contamination so far, an attempt was made to understand the existing scenario in terms of predominant heavy metals

Biological Treatment of Leachate using Sequencing Batch Reactor

Abstract   In Sri Lanka municipal solid waste is generally disposed in poorly managed open dumps which lack liner systems and leachate collection systems. Rain water percolates through the waste layers to produce leachate which drains in to ground water and finally to nearby water bodies, degrading the quality of water. Leachate thus has become a major environmental concern in municipal waste management and treatment of leachate is a major challenge for the existing and proposed landfill sites.   The study was conducted to assess the feasibility of the usage of the Sequencing Batch Reactor in the treatment of the landfill leachate up to the proposed levels in the draft report of “Proposed Sri Lankan standard for landfill leachate to be disposed to the inland waters". Leachate collected from the open dumpsite at Meethotamulla, Western Province, Sri Lanka was used for leachate characterization.   SBR was constructed with a 10-liter working volume operated in an 18 hour cycle mode and each cycle consists of 15hours of aerobic, 2h settle and 0.5 h of fill/decant stages. The Dissolved Oxygen level within the SBR was maintained at 2 mg/l through the aerobic stage. Infeed was diluted with water during the acclimatization period and a leachate to water ratio of 55:45 was maintained. The removal efficiencies for different parameters were; COD (90.5%), BOD (92.6%), TS (92.1%), Conductivity (83.9%), Alkalinity (97.4%), Hardness (82.2%), Mg (80.5%), Fe (94.2%), Zn (63.4%), Cr (31.69%), Pb (99.6%), Sulphate (98.9%), and Phosphorus (71.4%) respectively. In addition Ni and Cd were removed completely during a single SBR cycle. Thus the dilution of leachate in the dumpsites using municipal wastewater, groundwater or rainwater was identified as the most cost effective dilution methods. The effluent from the Sequencing batch reactor is proposed to be further treated using a constructed wetland before releasing to surface water.   Key Words- Sequencing batch Reactor (SBR), Leachate, Conceptual design, landfill    

Removal of iron (fe) from industrial wastewaters by constructed wetlands: an application of water Hyacinth (EICHHORNIA CRASSIPES (mart.) solms) stands

Severe contamination of water resources including groundwater with iron (Fe) due to various anthropogenic activities has been a major environmental problem in the industrial areas of Sri Lanka. At present Fe rich industrial' wastewaters are mostly treated with chemical precipitation. Moreover this technique is generally costly, depends on many intrinsic environmental parameters and requires intensive management and long-term maintenance. Hence the use of the obnoxious weed water hyacinth (Eichhornia crassipes (Mart.) Solms) in constructed wetlands to phytoremediate Fe rich wastewaters seems to be an appealing option. Although several studies have documented that hyacinths are good metal accumulating plants none of these studies have documented the effects of the nutritional status of the plants on the phytoremediation of metal rich industrial wastewaters. Hence in this paper we report the possible Fe removal efficiencies under different nutritional conditions of water hyacinth in batch type constructed wetlands. This study was conducted for 15 weeks by culturing water hyacinth in 590 I capacity fiberglass tanks under different nutrient concentrations of 2-fold (56 TN mg/l and 15.4 TP mg/l), l-fold, 112-fold, 114-fold and lI8-fold with Fe rich industrial wastewaters containing 9.27 Fe mg/l. A control set-up of hyacinths containing only Fe as a heavy metal but without any nutrients was also studied. A mass balance was conducted to investigate the phytoremediation efficiencies and to determine the different mechanisms governing Fe removal from the wastewater

Contribution of water hyacinth (Eichhornia crassipes (Mart.) Solms) grown under different nutrient conditions to Fe-removal mechanisms in constructed wetlands

Severe contamination of water resources including groundwater with iron (Fe) due to various anthropogenic activities has been a major environmental problem in industrial areas of Sri Lanka. Hence, the use of the obnoxious weed, water hyacinth (Eichhornia crassipes (Mart.) Solms) in constructed wetlands (floating aquatic macrophyte-based plant treatment systems) to phytoremediate Fe-rich wastewaters seems to be an appealing option. Although several studies have documented that hyacinths are good metal-accumulating plants none of these studies have documented the ability of this plant grown under different nutrient conditions to remove heavy metals from wastewaters. This paper, therefore, reports the phytoremediation efficiencies of water hyacinth grown under different nutrient conditions for Fe-rich wastewaters in batch-type constructed wetlands. This study was conducted for 15 weeks after 1-week acclimatization by culturing young water hyacinth plants (average height of 2072 cm) in 590 L capacity fiberglass tanks under different nutrient concentrations of 1-fold [28 and 7.7 mg/L of total nitrogen (TN) and total phosphorous (TP), respectively], 2-fold, 1/2-fold, 1/4-fold and 1/8-fold with synthetic wastewaters containing 9.27 Fe mg/L. Another set-up of hyacinths containing only Fe as a heavy metal but without any nutrients (i.e., 0-fold) was also studied. A mass balance was carried out to investigate the phytoremediation efficiencies and to determine the different mechanisms governing Fe removal from the wastewaters. Fe removal was largely due to phytoremediation mainly through the process of rhizofiltration and chemical precipitation of Fe2O3 and Fe(OH)3 followed by flocculation and sedimentation. However, chemical precipitation was more significant especially during the first 3 weeks of the study. Plants grown in the 0-fold set-up showed the highest phytoremediation efficiency of 47% during optimum growth at the 6th week with a highest accumulation of 6707 Fe mg/kg dry weight. Active effluxing of Fe back to the wastewater at intermittent periods and with time was a key mechanism of avoiding Fe phytotoxicity in water hyacinth cultured in all set-ups. Our study elucidated that water hyacinth grown under nutrient-poor conditions are ideal to remove Fe from wastewaters with a hydraulic retention time of approximately 6 weeks

Removal of aluminium by constructed wetlands with water hyacinth (Eichhornia crassipes (Mart.) Solms) grown under different nutritional conditions

This article reports the phytoremediation efficiencies of water hyacinth (Eichhornia crassipes (Mart.) Solms) grown under different nutritional conditions for Al rich wastewaters in batch type constructed wetlands (floating aquatic macrophyte-based plant treatment systems). This study was conducted for 15 weeks after 1 week acclimatization by culturing young water hyacinth (average height of 20 ± 2 cm) in 590 L capacity fiberglass tanks under different nutrient concentrations of 2-fold [56 and 15.4 mg/L of total nitrogen (TN) and total phosphorous (TP), respectively], 1-fold, 1/2-fold, 1/4-fold and 1/8-fold with synthetic wastewaters containing 5.62 Al mg/L. A control set-up of hyacinths comprising only Al with no nutrients was also studied. A mass balance was carried out to investigate the phytoremediation efficiencies and to identify the different Al removal mechanisms from the wastewaters. Chemical precipitation of Al(OH)3 was a dominant contribution to Al removal at the beginning of the study, whereas adsorption of Al3+ to sediments was observed to be a predominant Al removal mechanism as the study progressed. Phytoremediation mainly due to rhizofiltration was also an important mechanism of Al removal especially during the first 4 weeks of the study in almost all the set-ups. However, chemical precipitation and sediment adsorption of Al3+ was a dominant contribution to Al removal in comparison with phytoremediation. Plants cultured in the control set-up showed the highest phytoremediation efficiency of 63% during the period of the 4th week. A similar scenario was evident in the 1/8-fold set-up. Hence we conclude that water hyacinth grown under lower nutritional conditions are more ideal to commence a batch type constructed wetland treating Al rich wastewaters with a hydraulic retention time of approximately 4 weeks, after which a complete harvesting is recommended