Among wide range of membrane-based operations, membrane contactors, as they reify comparatively modern membrane-based mechanism are gaining quite an attention in both pilot and industrial scales. In recent literature, carbon capture is one of the most researched applications of membrane contactors. Membrane contactors have the potential to minimize the energy consumption and capital cost of traditional CO2 absorptions columns. In a membrane contactor, CO2 regeneration can take place below the solvent boiling point, resulting into lower consumption of energy. Various polymeric as well as ceramic membrane materials have been employed in gas liquid membrane contactors along with several solvents including amino acids, ammonia, amines etc. This review article provides detailed introduction of membrane contactors in terms of CO2 removal. It also discusses that the main challenge that is faced by membrane contactors is membrane pore wetting caused by solvent that in turn can reduce the mass transfer coefficient. Other potential challenges such as selection of suitable solvent and membrane pair as well as fouling are also discussed in this review and are followed by potential ways to reduce them. Furthermore, both membrane gas separation and membrane contactor technologies are analysed and compared in this study on the basis of their characteristics, CO2 separation performances and techno economical transvaluation. Consequently, this review provides an opportunity to thoroughly understand the working principle of membrane contactors along its comparison with membrane-based gas separation technology. It also provides a clear understanding of latest innovations in membrane contactor module designs as well as challenges encountered by membrane contactors along with possible solutions to overcome these challenges. Finally, semi commercial and commercial implementation of membrane contactors has been highlighted.
The objective of this study was to elucidate if chronic and acute ammonia intoxication in mudskippers, Periophthalmodon schlosseri and Boleophthalmus boddaerti, were associated with high levels of ammonia and/or glutamine in their brains, and if acute ammonia intoxication could be prevented by the administration of methionine sulfoximine [MSO; an inhibitor of glutamine synthetase (GS)] or MK801 [an antagonist of N-methyl D-aspartate type glutamate (NMDA) receptors]. For P. schlosseri and B. boddaerti exposed to sublethal concentrations (100 and 8 mmol l(-1) NH4Cl, respectively, at pH 7.0) of environmental ammonia for 4 days, brain ammonia contents increased drastically during the first 24 h, and they reached 18 and 14.5 micromol g(-1), respectively, at hour 96. Simultaneously, there were increases in brain glutamine contents, but brain glutamate contents were unchanged. Because glutamine accumulated to exceptionally high levels in brains of P. schlosseri (29.8 micromol g(-1)) and B. boddaerti (12.1 micromol g(-1)) without causing death, it can be concluded that these two mudskippers could ameliorate those problems associated with glutamine synthesis and accumulation as observed in patients suffering from hyperammonemia. P. schlosseri and B. boddaerti could tolerate high doses of ammonium acetate (CH3COONH4) injected into their peritoneal cavities, with 24 h LC50 of 15.6 and 12.3 micromol g(-1) fish, respectively. After the injection with a sublethal dose of CH3COONH4 (8 micromol g(-1) fish), there were significant increases in ammonia (5.11 and 8.36 micromol g(-1), respectively) and glutamine (4.22 and 3.54 micromol g(-1), respectively) levels in their brains at hour 0.5, but these levels returned to normal at hour 24. By contrast, for P. schlosseri and B. boddaerti that succumbed within 15-50 min to a dose of CH3COONH4 (15 and 12 micromol g(-1) fish, respectively) close to the LC50 values, the ammonia contents in the brains reached much higher levels (12.8 and 14.9 micromol g(-1), respectively), while the glutamine level remained relatively low (3.93 and 2.67 micromol g(-1), respectively). Thus, glutamine synthesis and accumulation in the brain was not the major cause of death in these two mudskippers confronted with acute ammonia toxicity. Indeed, MSO, at a dosage (100 microg g(-1) fish) protective for rats, did not protect B. boddaerti against acute ammonia toxicity, although it was an inhibitor of GS activities from the brains of both mudskippers. In the case of P. schlosseri, MSO only prolonged the time to death but did not reduce the mortality rate (100%). In addition, MK801 (2 microg g(-1) fish) had no protective effect on P. schlosseri and B. boddaerti injected with a lethal dose of CH3COONH4, indicating that activation of NMDA receptors was not the major cause of death during acute ammonia intoxication. Thus, it can be concluded that there are major differences in mechanisms of chronic and acute ammonia toxicity between brains of these two mudskippers and mammalian brains.
The objective of this study was to determine the effects of feeding on the excretory nitrogen (N) metabolism of the giant mudskipper, Periophthalmodon schlosseri, with special emphasis on the role of urea synthesis in ammonia detoxification. The ammonia and urea excretion rates of P. schlosseri increased 1.70- and 1.92-fold, respectively, within the first 3 h after feeding on guppies. Simultaneously, there were significant decreases in ammonia levels in the plasma and the brain, and in urea contents in the muscle and liver, of P. schlosseri at 3 h post-feeding. Thus, it can be concluded that P. schlosseri was capable of unloading ammonia originally present in some of its tissues in anticipation of ammonia released from the catabolism of excess amino acids after feeding. Subsequently, there were significant increases in urea content in the muscle, liver and plasma (1.39-, 2.17- and 1.62-fold, respectively) at 6 h post-feeding, and the rate of urea synthesis apparently increased 5.8-fold between 3 h and 6 h. Increased urea synthesis might have occurred in the liver of P. schlosseri because the greatest increase in urea content was observed therein. The excess urea accumulated in the body at 6 h was completely excreted between 6 and 12 h, and the percentage of waste-N excreted as urea-N increased significantly to 26% during this period, but never exceeded 50%, the criterion for ureotely, meaning that P. schlosseri remained ammonotelic after feeding. By 24 h, 62.7% of the N ingested by P. schlosseri was excreted, out of which 22.6% was excreted as urea-N. This is the first report on the involvement of increased urea synthesis and excretion in defense against ammonia toxicity in the giant mudskipper, and our results suggest that an ample supply of energy resources, e.g. after feeding, is a prerequisite for the induction of urea synthesis. Together, increases in nitrogenous excretion and urea synthesis after feeding effectively prevented a postprandial surge of ammonia in the plasma of P. schlosseri as reported previously for other fish species. Consequently, contrary to previous reports, there were significant decreases in the ammonia content of the brain of P. schlosseri throughout the 24 h period post-feeding, accompanied by a significant decrease in brain glutamine content between 12 h and 24 h.
Periophthalmodon schlosseri is an amphibious and obligatory air-breathing teleost, which is extremely tolerant to environmental ammonia. It actively excretes NH(4)(+) in ammonia loading conditions. For such a mechanism to operate efficaciously the fish must be able to prevent back flux of NH(3). P. schlosseri could lower the pH of 50 volumes (w/v) of 50% seawater in an artificial burrow from pH 8.2 to pH 7.4 in 1 day, and established an ambient ammonia concentration of 10 mmol l(-1) in 8 days. It could alter the rate of titratable acid efflux in response to ambient pH. The rate of net acid efflux (H(+) excretion) in P. schlosseri was pH-dependent, increasing in the order pH 6.0<7.0<8.0<8.5. Net acid flux in neutral or alkaline pH conditions was partially inhibited by bafilomycin, indicating the possible involvement of a V-type H(+)-ATPase. P. schlosseri could also increase the rate of H(+) excretion in response to the presence of ammonia in a neutral (pH 7.0) external medium. Increased H(+) excretion in P. schlosseri occurred in the head region where active excretion of NH(4)(+) took place. This would result in high concentrations of H(+) in the boundary water layer and prevent the dissociation of NH(4)(+), thus preventing a back flux of NH(3) through the branchial epithelia. P. schlosseri probably developed such an 'environmental ammonia detoxification' capability because of its unique behavior of burrow building in the mudflats and living therein in a limited volume of water. In addition, the skin of P. schlosseri had low permeability to NH(3). Using an Ussing-type apparatus with 10 mmol l(-1) NH(4)Cl and a 1 unit pH gradient (pH 8.0 to 7.0), the skin supported only a very small flux of NH(3) (0.0095 micromol cm(-2) min(-1)). Cholesterol content (4.5 micromol g(-1)) in the skin was high, which suggests low membrane fluidity. Phosphatidylcholine, which has a stabilizing effect on membranes, constituted almost 50% of the skin phospholipids, with phosphatidyleserine and phsophatidylethanolamine contributing only 13% and 15%, respectively. More importantly, P. schlosseri increased the cholesterol level (to 5.5 micromol g(-1)) and altered the fatty acid composition (increased total saturated fatty acid content) in its skin lipid after exposure to ammonia (30 mmol l(-1) at pH 7.0) for 6 days. These changes might lead to an even lower permeability to NH(3) in the skin, and reduced back diffusion of the actively excreted NH(4)(+) as NH(3) or the net influx of exogenous NH(3), under such conditions.
Untreated landfill leachate can harm the environment and human health due to its organic debris, heavy metals, and nitrogen molecules like ammonia. Microbial fuel cells (MFCs) have emerged as a promising technology for treating landfill leachate and generating energy. However, high concentrations of total ammonia-nitrogen (TAN), which includes both ammonia and the ammonium ion, can impede MFC performance. Therefore, maintaining an adequate TAN concentration is crucial, as both excess and insufficient levels can reduce power generation. To evaluate the worldwide research on MFCs using landfill leachate as a substrate, bibliometric analysis was conducted to assess publication output, author-country co-authorship, and author keyword co-occurrence. Scopus and Web of Science retrieved 98 journal articles on this topic during 2011-2022; 18 were specifically evaluated and analysed for MFC ammonia inhibition. The results showed that research on MFC using landfill leachate as a substrate began in 2011, and the number of related papers has consistently increased every 2 years, totaling 4060 references. China, India, and the USA accounted for approximately 60% of all global publications, while the remaining 40% was contributed by 70 other countries/territories. Chongqing University emerged as one of the top contributors among this subject's ten most productive universities. Most studies found that maintaining TAN concentrations in the 400-800 mg L-1 in MFC operation produced good power density, pollution elimination, and microbial acclimatization. However, the database has few articles on MFC and landfill leachate; MFC ammonia inhibition remains the main factor impacting system performance. This bibliographic analysis provides excellent references and future research directions, highlighting the current limitations of MFC research in this area.
Treatment of ammonia- and nitrate-rich wastewater, such as that generated in the aquaculture industry, is important to prevent environmental pollution. The anaerobic ammonium oxidation (anammox) process has been reported as a great alternative in reducing ammoniacal nitrogen concentration in aquaculture wastewater treatment compared to conventional treatment systems. This paper will highlight the impact of the anammox process on aquaculture wastewater, particularly in the regulation of ammonia and nitrogen compounds. The state of the art for anammox treatment systems is discussed in comparison to other available treatment methods. While the anammox process is viable for the treatment of aquaculture wastewater, the efficiency of nitrogen removal could be further improved through the proper use of anammox bacteria, operating conditions, and microbial diversity. In conclusion, a new model of the anammox process is proposed in this review.
Rivers as surface water in Malaysia are recipients of effluents and wastewater and yet it is important water source for daily uses of some villagers living along the river. Endocrine disruptors such as Bisphenol A (BPA) can be found in river due to continuous discharge into it. The objectives of this research is to find out the occurrence and concentration of BPA in Sungai Langat and also to see how water quality parameters such as temperature, pH, dissolved oxygen (DO), turbidity, Total Suspended Solid (TSS), Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD) and ammonia nitrogen (AN) affecting the concentration of BPA. 12 stations in total including upstream to downstream of Sungai Langat and also tributary of Sungai Langat. The instrument used to find out concentration of BPA is Triple Quadrupole LC/MS. The source of BPA are mainly industrial effluents and also direct domestic discharges. The water quality parameters that will affect concentration of BPA are Ammonia Nitrogen (AN), turbidity, Biochemical Oxygen Demand (BOD), Total Suspended Solid (TSS), and Chemical Oxygen Demand (COD), Dissolved Oxygen (DO). While pH and water temperature are also factors that will affect concentration of BPA but the significance is not shown in the analysis. It can be concluded that upstream of Sungai Langat has lower concentration of BPA than downstream.
A split plot 3 × 3 experiment was designed to examine the impact of three concentrations of CO₂ (400, 800 and 1,200 μmol·mol⁻¹) on the phenolic and flavonoid compound profiles, phenylalanine ammonia lyase (PAL) and antioxidant activity in three varieties of Labisia pumila Benth. (var. alata, pumila and lanceolata) after 15 weeks of exposure. HPLC analysis revealed a strong influence of increased CO₂ concentration on the modification of phenolic and flavonoid profiles, whose intensity depended on the interaction between CO₂ levels and L. pumila varieties. Gallic acid and quercetin were the most abundant phenolics and flavonoids commonly present in all the varieties. With elevated CO₂ (1,200 μmol·mol⁻¹) exposure, gallic acid increased tremendously, especially in var. alata and pumila (101-111%), whilst a large quercetin increase was noted in var. lanceolata (260%), followed closely by alata (201%). Kaempferol, although detected under ambient CO₂ conditions, was undetected in all varieties after exposure. Instead, caffeic acid was enhanced tremendously in var. alata (338~1,100%) and pumila (298~433%). Meanwhile, pyragallol and rutin were only seen in var. alata (810 μg·g⁻¹ DW) and pumila (25 μg·g⁻¹ DW), respectively, under ambient conditions; but the former compound went undetected in all varieties while rutin continued to increase by 262% after CO₂ enrichment. Interestingly, naringenin that was present in all varieties under ambient conditions went undetected under enrichment, except for var. pumila where it was enhanced by 1,100%. PAL activity, DPPH and FRAP also increased with increasing CO₂ levels implying the possible improvement of health-promoting quality of Malaysian L. pumila under high CO₂ enrichment conditions.
A randomized complete block design 2 × 4 experiment was designed and conducted for 15 weeks to characterize the relationships between production of total phenolics, flavonoid, anthocyanin, leaf gas exchange, total chlorophyll, phenylalanine ammonia-lyase (PAL) and malondialdehyde (MDA) activity in two varieties of Labisia pumila Benth, namely the var. alata and pumila, under four levels of evapotranspiration replacement (ER) (100%; well watered), (75%, moderate water stress), (50%; high water stress) and (25%; severe water stress). The production of total phenolics, flavonoids, anthocyanin, soluble sugar and relative leaf water content was affected by the interaction between varieties and SWC. As the ER levels decreased from 100% to 25%, the production of PAL and MDA activity increased steadily. At the highest (100%) ER L. pumila exhibited significantly higher net photosynthesis, apparent quantum yield, maximum efficiency of photosystem II (f(v)/f(m)) and lower dark respiration rates compared to the other treatment. The production of total phenolics, flavonoids and anthocyanin was also found to be higher under high water stress (50% ER replacement) compared to severe water stress (25% ER). From this study, it was observed that as net photosynthesis, apparent quantum yield and chlorophyll content were downregulated under high water stress the production of total phenolics, flavonoids and anthocyanin were upregulated implying that the imposition of high water stress can enhance the medicinal properties of L. pumila Benth.
The present study deals with the assessment of Langat River water quality with some chemometrics approaches such as cluster and discriminant analysis coupled with an artificial neural network (ANN). The data used in this study were collected from seven monitoring stations under the river water quality monitoring program by the Department of Environment (DOE) from 1995 to 2002. Twenty three physico-chemical parameters were involved in this analysis. Cluster analysis successfully clustered the Langat River into three major clusters, namely high, moderate and less pollution regions. Discriminant analysis identified seven of the most significant parameters which contribute to the high variation of Langat River water quality, namely dissolved oxygen, biological oxygen demand, pH, ammoniacal nitrogen, chlorine, E. coli, and coliform. Discriminant analysis also plays an important role as an input selection parameter for an ANN of spatial prediction (pollution regions). The ANN showed better prediction performance in discriminating the regional area with an excellent percentage of correct classification compared to discriminant analysis. Multivariate analysis, coupled with ANN, is proposed, which could help in decision making and problem solving in the local environment.
Oil palm fronds are the most abundant lignocellulosic biomass in Malaysia. In this study, fronds were tested as the potential renewable biomass for ethanol production. The soaking in aqueous ammonia pretreatment was applied, and the fermentability of pretreated fronds was evaluated using simultaneous saccharification and fermentation. The optimal pretreatment conditions were 7 % (w/w) ammonia, 80 °C, 20 h of pretreatment, and 1:12 S/L ratio, where the enzymatic digestibility was 41.4 % with cellulase of 60 FPU/g-glucan. When increasing the cellulase loading in the hydrolysis of pretreated fronds, the enzymatic digestibility increased until the enzyme loading reached 60 FPU/g-glucan. With 3 % glucan loading in the SSF of pretreated fronds, the ethanol concentration and yield based on the theoretical maximum after 12 and 48 h of the SSF were 7.5 and 9.7 g/L and 43.8 and 56.8 %, respectively. The ethanol productivities found at 12 and 24 h from pretreated fronds were 0.62 and 0.36 g/L/h, respectively.
Ammonium-enriched skim latex serum - used for absorption of contaminating ammonia gas - when composted with other rubber tree wastes, is promising as a good compost. The objective of this research was to utilize ammonium-enriched skim latex serum (S) as a raw composting ingredient after being combined with para sawdust (W1) and para rubber leaves (W2). Several ratios of S, W1 and W2 were experimented in a 15L composting vessel to determine the most effective compost. The best ratio was found to be 3:1:3 by weight at 12-day retention. The modified 30 L composting reactor employed with the derived optimum mixing conditions yielded N, P and K of 2.40, 1.51 and 14.84 %w/w. The growth of Brassica alboglabra after application of this compost combined with a chemical fertilizer generated the highest fresh weight (4.48 g/plant). Thus, compost from these wastes could be used as a fertilizer and logically should contribute to cost saving of waste disposal.
In this study, two native duckweeds (Lemna minor and Azolla pinnata) were cultivated in Palm Oil Mill Effluent (POME) to extract nutrients from the effluent. Five grams of A. pinnata and 2 g of L. minor were transferred to 2 L POME (Initial concentrations: 198 mg/L COD, 4.3 mg/L nitrates, pH 9.53, 4 mg/L phosphate, 2.98 mg/L ammonia) with four different dilutions (2.5%, 5%, 10%, 15%) under greenhouse conditions. Samples of POME were taken every two days up to 10 days. Growth parameter, phosphate, ammonia, nitrates, pH, and COD were monitored within 10 days to select the most suitable growth medium for both plants. Results showed that 2.5% POME dilution had positive effect on L. minor growth and A. pinnata (wet weight increased by 8.7 g and 9.8 g, respectively), with all plants able to survive until the final day of exposure. The highest removal of ammonia was accomplished in 5% POME dilution by A. pinnata (98%) and L. minor (95.5%). The maximum phosphate removal was obtained in 10% POME dilution with 93.3% removal by A. pinnata and 86.7% by L. minor. Significant COD removal in 15% POME was obtained by L. minor (78%) and A. pinnata (66%). Both plants responded positively to the phytoremediation process, especially for A. pinnata which showed significant decreases in all parameters. The nutrient extraction by both plants from POME showed a positive effect on growth parameter, which has further promising potential to be used as animal feedstock.
Assessment of the treatment performance in the field-scale hybrid constructed wetland (CW) for ammonia manufacturing plant remains limited. After being in operations running on and off since 2014, the hybrid CW which treats effluent from the ammonia manufacturing plant in Peninsular, Malaysia has recently demonstrated the full clogging to the CW. It takes only 8 months to demonstrate a big deterioration of performance in 2019. Though the mechanism of clogging is not clear, which can be partially from inherent design problems or operational issues, nonetheless, it is important to evaluate how this clogging has impacted the effluent treatment performance and the continuous utilization of the CW. The purpose of this study is to evaluate the impact of the treatment performance on the ammoniacal nitrogen and COD removal when the CW is clogged. The result revealed that there is no impact on COD removal, but it has a substantial impact on the ammoniacal nitrogen removal. The ammoniacal nitrogen removal dropped to negative (outlet concentration is higher than inlet concentration) during the clogged period. Another observation is, the low removal rate also coincides with a high COD/N ratio, when the COD/N ratio increased to >2, the ammoniacal nitrogen removal rate dropped substantially, with the coefficient of determination, R2 of 40.5%. The root cause for the clogging to develop in a short period of time is unidentified. However, it is still worth noting that COD and ammoniacal nitrogen efficiency did not behave the same at the clogged CW.
Air pollution can be detected through rainwater composition. In this study, long-term measurements (2000-2014) of wet deposition were made to evaluate the physicochemical interaction and the potential sources of pollution due to changes of land use. The rainwater samples were obtained from an urban site in Kuala Lumpur and a highland-rural site in the middle of Peninsular Malaysia. The compositions of rainwater were obtained from the Malaysian Meteorological Department. The results showed that the urban site experienced more acidity in rainwater (avg=277mm, range of 13.8 to 841mm; pH=4.37) than the rural background site (avg=245mm, range of 2.90 to 598mm; pH=4.97) due to higher anthropogenic input of acid precursors. The enrichment factor (EF) analysis showed that at both sites, SO42-, Ca2+ and K+ were less sensitive to seawater but were greatly influenced by soil dust. NH4+ and Ca2+ can neutralise a larger fraction of the available acid ions in the rainwater at the urban and rural background sites. However, acidifying potential was dominant at urban site compared to rural site. Source-receptor relationship via positive matrix factorisation (PMF 5.0) revealed four similar major sources at both sites with a large variation of the contribution proportions. For urban, the major sources influence on the rainwater chemistry were in the order of secondary nitrates and sulfates>ammonium-rich/agricultural farming>soil components>marine sea salt and biomass burning, while at the background site the order was secondary nitrates and sulfates>marine sea salt and biomass burning=soil components>ammonia-rich/agricultural farming. The long-term trend showed that anthropogenic activities and land use changes have greatly altered the rainwater compositions in the urban environment while the seasonality strongly affected the contribution of sources in the background environment.
The primary biological treatment method for organic sludge is composting and/or anaerobic digestion, but their product (compost or biogas) is of little economic benefit; therefore, an improved process to produce a high-value product is required to make sludge management more sustainable. Maximizing NH3 gas recovery during composting processes has the potential benefit of producing high-value microalgal biomass. However, the majority of produced ammonia does not evaporate as NH3 gas but retains as NH4+-N in the compost after fermentation. The present study investigates the effects of the timing of Ca(OH)2 dosing (on days 2, 5, and 9), and the Ca(OH)2 dose (1.1-2.6 mmol/batch), on lab-scale thermophilic composting of anaerobic sludge. The effects on NH3 recovery, organic matter degradability, and microbial activity are evaluated. Ca(OH)2 dosing immediately improved the emission of NH3, with yields 50-69% higher than those under control conditions. The timing of the dosing did not influence NH3 recovery or organic matter degradability. Higher Ca(OH)2 doses resulted in higher NH3 recovery, while microbial activity was temporarily and marginally inhibited. The pH of the compost reached 10-11.5 but quickly dropped to 8-8.5 within a day, probably because of neutralization of Ca(OH)2 by the emitted CO2 and release of NH3, which maintained the microbial activity. The present study indicated that Ca(OH)2 dosing would be useful to apply during thermophilic composting for NH3 recovery to cultivate high-value microalgal biomass, which enables this process to obtain a more economic benefit.
Development of thermophilic composting for maximizing NH3 gas recovery would enable the production of a nitrogen source which is free from pathogen/heavy metal, for the cultivation of high-value microalgae. The present study examined the effect of NH3 recovery, nitrogen mass balance, and microbial community dynamics on thermophilic composting of shrimp aquaculture sludge. The emission of NH3 gas at 60 and 70 °C was 14.7% and 15.6%, respectively, which was higher than that at 50 °C (9.0%). The nitrogen mass balance analysis revealed that higher temperatures enhanced the solubilization of non-dissolved nitrogen and liberation of NH3 gas from the produced NH4+-N. High-throughput microbial community analysis revealed the shift of the dominant bacterial group from Bacillus to Geobacillus with the rise of composting temperature. In conclusion, thermophilic composting of shrimp aquaculture sludge at 60-70 °C was the most favorable condition for enhancing NH3 gas recovery.
In the past few decades, there has been a rapid growth in the concentration of nitrogenous compounds such as nitrate-nitrogen and ammonia-nitrogen in rivers, primarily due to increasing agricultural and industrial activities. These nitrogenous compounds are mainly responsible for eutrophication when present in river water, and for 'blue baby syndrome' when present in drinking water. High concentrations of these compounds in rivers may eventually lead to the closure of treatment plants. This study presents a training and a selection approach to develop an optimum artificial neural network model for predicting monthly average nitrate-N and monthly average ammonia-N. Several studies have predicted these compounds, but most of the proposed procedures do not involve testing various model architectures in order to achieve the optimum predicting model. Additionally, none of the models have been trained for hydrological conditions such as the case of Malaysia. This study presents models trained on the hydrological data from 1981 to 2017 for the Langat River in Selangor, Malaysia. The model architectures used for training are General Regression Neural Network (GRNN), Multilayer Neural Network and Radial Basis Function Neural Network (RBFNN). These models were trained for various combinations of internal parameters, input variables and model architectures. Post-training, the optimum performing model was selected based on the regression and error values and plot of predicted versus observed values. Optimum models provide promising results with a minimum overall regression value of 0.92.
The stabilization mechanism of natural rubber (NR) latex from Hevea brasiliensis was studied to investigate the components involved in base-catalyzed ester hydrolysis, namely, hydrolyzable lipids, ammonia, and the products responsible for the desired phenomenon observed in ammonia-preserved NR latex. Latex stability is generally thought to come from a rubber particle (RP) dispersion in the serum, which is encouraged by negatively charged species distributed on the RP surface. The mechanical stability time (MST) and zeta potential were measured to monitor field latices preserved in high (FNR-HA) and low ammonia (FNR-LA) contents as well as that with the ester-containing components removed (saponified NR) at different storage times. Amounts of carboxylates of free fatty acids (FFAs), which were released by the transformation and also hypothesized to be responsible for the like-charge repulsion of RPs, were measured as the higher fatty acid (HFA) number and corroborated by confocal laser scanning microscopy (CLSM) both qualitatively and quantitatively. The lipids and their FFA products interact differently with Nile red, which is a lipid-selective and polarity-sensitive fluorophore, and consequently re-emit characteristically. The results were confirmed by conventional ester content determination utilizing different solvent extraction systems to reveal that the lipids hydrolyzed to provide negatively charged fatty acid species were mainly the polar lipids (glycolipids and phospholipids) at the RP membrane but not those directly linked to the rubber molecule and, to a certain extent, those suspended in the serum. From new findings disclosed herein together with those already reported, a new model for the Hevea rubber particle in the latex form is proposed.
Black pepper production in Malaysia was restricted by various diseases. Hazardous chemical products appear to be the best solution to control diseases in black pepper cultivation. However, persistence of chemical residues in peppercorns could affect the quality of exports and consumptions. Application of fertilizers is crucial to sustain pepper growth and high yield. But, continuous use of chemical fertilizers could affect the soil ecosystem and eventually restrict nutrient uptake by pepper roots. Therefore, we propose biological approaches as an alternative solution instead of chemical products to sustain pepper cultivation in Malaysia. In this study, we have isolated a total of seven indigenous rhizobacteria antagonistic to soil-borne Fusarium solani, the causal fungus of slow decline, the most serious debilitating disease of black pepper in Malaysia. The isolated bacteria were identified as Bacillus subtilis, Bacillus siamensis, Brevibacillus gelatini, Pseudomonas geniculata, Pseudomonas beteli, Burkholderia ubonensis and Burkholderia territorii. These bacteria were effective in production of antifungal siderophore with the amount of 53.4 %-73.5 % per 0.5 mL of cell-free supernatants. The bacteria also produced appreciable amount of chitinase with chitinolytic index was ranged from 1.19 to 1.76. The bacteria have shown phosphate solubilizing index within 1.61 to 2.01. They were also efficient in ACC deaminase (0.52 mM-0.62 mM) and ammonia (60.3 mM-75.3 mM) production. The isolated antagonists were efficacious in stimulation of black pepper plant growth and root development through IAA (10.5 μg/mL-42.6 μg/mL) secretion. In conclusion, the isolated rhizobacteria are potent to be developed not only as biocontrol agents to minimize the utilization of hazardous chemicals in black pepper disease management, but also developed as bio-fertilizers to improve black pepper plant growth due to their capabilities in plant growth-promotion.