Application of forward osmosis for the reduction of pre-treatment sludge volume in desalination: modelling and experiments.

Forward osmosis (FO) is a novel water treatment process that potentially can be used as an alternative technology for both sludge and brine treatment due to its low energy requirement. In the FO process, a solution of high salt concentration (known as draw solution) is utilized to generate an osmotic pressure gradient across a semipermeable membrane to extract freshwater from a solution with lower salt concentration (known as feed solution). The FO process requires low energy to operate as it capitalizes on the phenomenon of natural osmosis. FO has been given significant attention over the past few years due its superior characteristics. However, this technology is still in the developmental stages. A few studies have been carried out using FO for the treatment of industrial wastewater, landfill leachate and food industry effluents. However, to date, there has been no research on sludge treatment and brine management using the FO process, other than this research, which could be another promising application of FO. Therefore, in this study FO was proposed as an additional process to the seawater reverse osmosis (RO) process to dilute the brine before it is discharged back to the ocean and to reduce the volume of pre-treatment sludge before mechanical dewatering. Diluting of brine have number of advantages depending on the industrial requirements such as (1) it can increase the brine diffusion rate as the concentration is low (2) it can keep the same diffusion rate however adverse effect to flora and fauna near the diffusers are low as the salt concentration is low (3) it can be sent back to the RO desalting process to increase the overall water recovery as the diluted brine is already pre-treated. Most of the current seawater desalination plants have two-stage reverse osmosis (RO) processes. Therefore, the proposed FO systems utilize 1st stage RO concentrate (brine) as the draw solution (since osmotic pressure of brine is higher due to higher salinity) and pre-treatment sludge as feed solution (lower salt concentration). After passing through the FO system, as a consequence of water permeation from feed to draw solution, the pre-treatment sludge volume becomes lower and the brine gets diluted. Diluted brine can either be sent back to the 1st pass RO process to increase the overall water recovery or blended with the 2nd pass RO brine before being discharged to the ocean. By doing the latter, the diffusion rate of the brine within the water body can be increased. In this study, laboratory experiments to assess the viability of applying the FO process for an RO desalination system at different sludge conditions (pH, temperature) were conducted. Further, biofilm growth on the membrane surface up to 8 weeks of continuous filtration was analysed. In addition, mass balance calculations were used to predict the reduced sludge volume and power requirement arising from large scale (340 ML/day intake) and small scale (15 ML/day intake) hybrid FO/RO desalination plants. The electrical conductivity (EC) of the brine and seawater EC were 73.0 mS/cm and 44.5 mS/cm, respectively. As EC is directly proportional to osmotic pressure, there was a sufficient osmotic pressure difference between the draw and feed solutions to have adequate water flux through the FO system. However, the total organic carbon (TOC) of the brine and sludge were 3.10 mg/L and 8.92 mg/L, respectively. Therefore, there is a potential for biofilm growth on the membrane surface. When the pH of feed solution was increased from 6 to 8, there was a marginal change in water flux. Therefore, the as is pH (normally pH 8) of feed solution is recommended for the hybrid system. When the temperature increased from 20 to 40 oC, the average water flux slightly increased (5.6 to 6.0 LMH). However, considering the economic benefits, it is recommended to operate at room temperature. The water flux of continuous filtration experiments declined with time due to fouling as well as dilution of the draw solution. However, flux increased when the draw and feed solutions were replaced with the fresh solutions. This increased flux was lower than the initial flux of the previous batch and was due to fouling on the membrane. After one week of filtration, the flux declined further due to the thickened fouling layer deposited on the membrane. The layer may have contained microorganisms in addition to salt deposits as both draw and feed solutions contained salt ions. However, scanning electron microscopy (SEM) spectrum showed salt deposits on the membrane surface after 5 week of continuous filtration without cleaning in between. This fouling can easily be overcome by providing regular flushes at high cross flow velocities as deposited layers are thin and loose and therefore readily removed. After 8 weeks of continuous filtration large salt deposits were observed. Further, after 8 weeks there was no water permeation through membrane. After analysing SEM EDX images and spectra, weekly membrane cleaning is recommended to avoid biofouling and inorganic fouling. After analysing water flux values and the fouling behaviour during FO filtration, mathematical modelling was carried out for the proposed RO/FO systems. Since, daily pre-treatment sludge generation varies (both in volume and solids content) with the desalination plant size, calculations were made for two plant sizes: large-scale plants (LSP, 340 ML / day intake) and small-scale plants (SSP, 15 ML / day intake). When the membrane area is 100 m2 (minimum area considered in this study) it can reduce sludge volume up to 7% in a SSP, however this depends on the water flux through FO. When the membrane area increases, sludge volume reduction increases in both large and small scale plants. The sludge solids content can be increased from 3 to 10% TS with a small power requirement (17.3 kW h /day). Interestingly, when the membrane area of a LSP is increased to 900 m2, the sludge volume is reduced by 50%. This yields a sludge stream having a final solids content of 7.6%. Proposed system requires lower OPEX and CAPEX compared to existing system; however, they are marginal. With all the results obtained through laboratory scale experiments and mathematical modelling, it is evident that the proposed hybrid system is a promising technology to reduce the volume of pre-treatment sludge and increase the overall water recovery of RO process

EFFECT OF DIFFERENT LEVELS OF SALINITY ON GROWTH PERFORMANCES OF FOUR SELECTED TREE SPECIES

Salt affected soils are widespread in different parts of the world. In recent years significantamount of land extent were affected due to salinity rendering them biologically unproductive.The use of specific techniques for tnc amelioration of these lands for agriculture is taking placecontinuously. Reforestation of salt affected soils is possible given proper site preparation, choiceof suitable salt tolerant species and their proper nursery and cultural practices are achieved. Thepotentials of these soils for growing trees and woody vegetation have not been fully exploredyet.Therefore, four different pot experiments were conducted by using four selected tree speciesmainly available in the salt affected areas (i.e, Tamarind (Tamarindus indica), Katuandara(At:acia /eucop/oea), Castor (Ricinus communis) and Wood apple (Feronia /imonia) at theFaculty of Agriculture, University of Ruhuna Mapalana, Kamburupitiya during April to October200 1 to assess the influences of different levels of saline water (i.e. 0.13,2,4,6,8 and 12mmhos/cm) on growth and development of above four tree species. All the experiments wereconducted by using a Randomized Complete Design with four replicates. One month oldseedling raised in 6"x8" size polythene bags were used for the experiment. Seedlings weretransferred to lager Polythine bags (lO"x 12") at 2 months after planning without damage to theroot system to ensure enough space for root development. Plant height, shoot and root biomassyield were measured at every 2 weeks interval.The result revealed that the plant height, shoot and root biomass yield were not affectedsignificantly by different levels of saline water up to 12 mmhos /cm compared to the controlwhere normal water (O.13mmhosl em) is applied in all crop species. Therefore all four-treespecies, which were used for the experiment, may be recommended as salt tolerant tree speciesup salinity to the level of 12rnmhos/cm.

Influence of undergraduates activities on the waste composition and generation rates in a residential University – case study

The increase of waste generation and its disposal is a major problem and challenge faced by the most of the countries today.The uncontrolled disposal of different types of waste into environment is a great threat for the future of all living beings in the world. Therefore, it is essential to pay more attention for the waste management and disposal to avoid the detrimental impact on the environment. For the development of a proper treatment or disposal systems for waste management for any organization or municipality, it is essential to have the information with respect to waste composition, generation rate and its variation with time of that organization. Therefore, in this study, it was attempted to evaluate the composition and the variation of waste generation rate in the hostels of the undergraduates of University of Ruhuna with their activities.The study was conducted in the premises and surroundings of the hostels of the undergraduates for a period of one year (September to August). The waste samples were collected from each and every hostel once in two months. The waste samples were separated into different components (such as foods, paper, plastics, etc), weighed and determined the percentages of different components.  The different types of waste generation rate per head were calculated based on the waste generation for the total study period. It was found that food remains, papers, plastics and polythene are the major components. The types of waste found in hostels of girls were less in numbers than that of boys. Leather, textiles, metals, etc could not be found in hostels of girls.Over ~95 % of waste found in girls’ hostels were food remains and boys generate food waste about ~71%. Per capita food waste generation by girls was ~ 207 g/day while it was ~23 g/day by boys. The generation of other types of waste was higher in hostels of boys than that of girls’ hostels. It appears that the amount of waste generation varied in different months basically due to examinations and other activities of the students. During examination periods, it seems that the undergraduates may change their food habits. Based on this study, it can be concluded that major component of waste found in undergraduate hostels was food wastes and the generation rate slightly varies with the activities of undergraduates. When designing of a waste management systems for higher education institutes where students reside, higher priority should be given for the management of food wast

A preliminary study on the volume reduction of pre-treatment sludge in seawater desalination by forward osmosis

Forward Osmosis (FO) can be applied to recover water from the pre-treatment sludge of seawater reverse osmosis process. This study investigated the effect of the concentration of two draw solutions (MgCl2 and NaCl) in the reduction of Fe(OH)3 sludge volume and the effect of cross flow velocity on flux through FO membrane. Higher the concentration of NaCl and MgCl2 higher the water flux observed. However, the percentage increase was not significant due to the occurrence of internal concentration polarisation. MgCl2 draws marginally increased water flux than NaCl, when the conditions of feed and draw solutions were similar. Increase in cross flow velocity (from 0.25 to 1.0&thinsp;m/s) marginally changed the flux with both draw solutions as higher cross flow velocities were unproductive to beat the external CP effect along the membrane surface. However, at 1&thinsp;m/s, highest fluxes were obtained for both draw solutions.<br /

MANAGING THE TOURISM-LED DEVELOPMENT STRATEGY IN POST-WAR SRI LANKA

The Sri Lankan tourism industry has been booming since the end of war in 2009. Considering the key role that tourism can play in post-war economic development, the Sri Lankan government launched a Tourism Development Strategy (TDS). This study has evaluated the feasibility of achieving the targets of the TDS by building a simple tourism demand model and by undertaking a qualitative comparative assessment with a selected tourism booms in a number of war-affected countries. The findings suggest that the TDS targets are achievable provided the country manages to expand supply of tourism related infrastructure (hard as well as soft) in a price competitive manner

Determination of the optimal pre-processing technique for spectral data of oil palm leaves with respect to nutrient

Precision agriculture with regard to crop science was introduced to apply only the required and optimal amount of fertiliser, which inspired the present study of nutrient prediction for oil palm using spectroradiometer with wavelengths ranging from 350 to 2500 nm. Partial least square (PLS) method was used to develop a statistical model to interpret spectral data for nutrient deficiency of nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), calcium (Ca) and boron (B) of oil palm. Prior to the development of the PLS model, pre-processing was conducted to ensure only the smooth and best signals were studied, which includes the multiplicative scatter correction (MSC), first and second derivatives and standard normal variate (SNV), Gaussian filter and Savitzky-Golay smoothing. The MSC technique was the optimal overall pre-treatment method for nutrients in this study, with highest prediction R2 of 0.91 for N and lowest RMSEP value of 0.00 for P

Should colloid boluses be prioritized over crystalloid boluses for the management of dengue shock syndrome in the presence of ascites and pleural effusions?

<p>Abstract</p> <p>Background</p> <p>Although the WHO guideline for the management of dengue fever considers the presence of ascites or pleural effusions in the diagnosis of DSS, it does not emphasize the importance of their presence when selecting fluids for resuscitation.</p> <p>Case presentation</p> <p>We highlight three patients with DSS who received boluses of crystalloids on priority basis as recommended by WHO guidelines during resuscitation. All three patients had varying degrees of third space fluid loss (ascites and pleural effusions) at the time of development of DSS. Ascites and pleural effusions were detected in all 3 patients at the time of shock irrespective of whether iv fluids were given or not. All three patients had documented liver involvement at the time of shock evidenced by elevation of AST (4800 iu/L, 5000 iu/L and 1960 iu/L). One patient who had profound shock died 6 hours after admission with evidence of acute pulmonary oedema in the convalescence phase. All of them needed CPAP ventilator support and potent diuretics.</p> <p>Conclusions</p> <p>We therefore feel that resuscitation of patients with DSS who already have third space fluid accumulation with crystalloid boluses on priority basis may contribute to recovery phase pulmonary oedema.</p

Hybrid coating on a magnesium alloy for minimizing the localized degradation for load-bearing biodegradable mini-implant applications

The effect of a hybrid coating, calcium phosphate (CaP) + polylactic acid (PLA), on a magnesium alloy on its in vitro degradation (general and localized) behaviour was studied for potential load-bearing biodegradable mini-implant applications. CaP was coated on a magnesium alloy, AZ91, using an electrochemical deposition method. A spin coating method was used to coat PLA on the CaP coated alloy. In vitro degradation performance of the alloy with hybrid coating was evaluated using electrochemical impedance spectroscopy (EIS) in simulated body fluid (SBF). The EIS results showed that the hybrid coating enhanced the degradation resistance of the alloy by more than two-order of magnitude as compared to the bare alloy and one-order of magnitude higher than that of the CaP coated alloy, after 1 h exposure in simulated body fluid (SBF). Long-term (48 h) EIS results also confirmed that the hybrid coating performed better than the bare alloy and the CaP coated alloy. Importantly, the hybrid coating improved the localized degradation resistance of the alloy significantly, which is critical for better in service mechanical integrity

Polylactic acid coating on a biodegradable magnesium alloy: an in vitro degradation study by electrochemical impedance spectroscopy

Polylactic acid (PLA) was coated on a biodegradable magnesium alloy, AZ91, using spin coating technique for temporary implant applications. The degradation behaviour of the coated alloy samples was evaluated using electrochemical impedance spectroscopy (EIS) method in simulated body fluid (SBF). EIS results suggested that the PLA coating enhanced the degradation resistance of the alloy significantly. Increase in the PLA coating thickness was found to increase the degradation resistance, but resulted in poor adhesion. Long-term EIS experiments of the PLA coated samples suggested that their degradation resistance gradually decreased with increase in SBF exposure time. However, the degradation resistance of the PLA coated samples was significantly higher than that of the bare metal even after a 48 h exposure to SBF

A Quantitive Evaluation of the Potential Effects of Trade Policy Reversal in Sri Lanka: A Computable General Equilibrium (CGE) Analysis

In recent years there has been a trend in rising protectionism and a reversal of trade policy reforms in some developed and developing countries, particularly after the global financial crisis. Although some researchers and practitioners have discussed recent trends in trade policy reversal in both developed and developing countries in recent years, no serious attempts have been made to examine the effects of trade policy reversal in a developing country within an economy-wide framework. The current paper attempts to fill this research gap by answering the question: Can developing countries benefit from trade policy reversals? The study focuses particularly on the case of Sri Lanka. To address this central research aim the paper first reviews recent trends in import duty and para-tariffs in Sri Lanka, particularly after the global financial crisis. An economy-wide computable general equilibrium (CGE) model was then used to evaluate the effects of trade policy reversal on the Sri Lankan economy. The results of the Sri Lankan case study presented suggest that developing countries will not benefit from trade policy reversal at either the macro level or industry level