Overpopulation and rapid development have put an increasing burden on the environment, leading to various water crisis. Importing water from abandoned mines as an alternative raw water source could be the next answer to alleviate water scarcity problems globally. However, due to its high heavy metals content, there is a need to find an economical and effective method to remove heavy metals before reusing it as potable water source. Biochar, a low-cost and carbon-rich biosorbent, has received increasing attention on its application as a remediating agent to remove heavy metals from water. Previous studies have revealed the potential properties of biochar as a heavy metal removal agent including high cation exchange capacity, high surface area, active surface functional groups, as well as efficient adsorption. Apparently, the most important factor influencing the sorption mechanism is the type of feedstock materials. Spent mushroom compost (SMC), a waste product from mushroom cultivation, has been found as an excellent biosorbent. SMC has received global attention as it is low cost and eco-friendly. It also has been proved as an efficient heavy metals remover from water. Nevertheless, its application as biochar is still scarce. Therefore, this review focuses on the potential of transforming SMC into modified biochar to remove heavy metals, especially from abandoned mining water. The present review emphasizes the current trends in adsorption methods for heavy metal removal from water, assembles data from previous studies on the feedstock of biosorbents to biochars, and discusses the potentials of SMC as a biochar for water treatment.
Rapid industrial developments coupled with surging population growth have complicated issues dealing with water scarcity as the quest for clean and sanitized water intensifies globally. Existing fresh water supplies could be contaminated with organic, inorganic and biological matters that have potential harm to the society. Turbidity in general is a measure of water cloudiness induced by such colloidal and suspended matters and is also one of the major criteria in raw water monitoring to meet the stipulated water quality guidelines. Turbidity reduction is often accomplished using chemical coagulants such as alum. The use of alum is widely associated with potential development of health issues and generation of voluminous sludge. Natural coagulants that are available in abundance can certainly be considered in addressing the drawbacks associated with the use of chemical coagulants. Twenty one types of plant-based natural coagulants categorized as fruit waste and others are identified and presented collectively with their research summary in this review. The barriers and prospects of commercialization of natural coagulants in near future are also discussed.
The redfleshed pulp discarded from pink guava puree industry is a rich source of lycopene and pectin. In this study, we developed a facile extraction process employing water as the primary extraction medium to isolate the lycopene and pectin from pink guava decanter. When the decanter was suspended in water, the complexation of lycopene and pectin formed the cloudy solution, where the colloidal complexes were recovered through centrifugation. The presence of lycopene and pectin in the complex was confirmed by the spectroscopic, microscopic and chromatographic analyses. The lycopene fractionated from the complexes had a purity level of 99% and was in all-trans configuration. The colloidal complexes yielding the highest concentration of lycopene was obtained at pH 7, 1% (w/v) solid loading and 25 °C. The experimental data of time-course extraction of lycopene-pectin complex were best fitted with two-site kinetic model, hinting the fast- and slow-release phases in the extraction process.
Using waste rubber tires for concrete production will reduce the demand for natural aggregate and help to reduce environmental pollution. The main challenge of using waste rubber tires in concrete is the deterioration of mechanical properties, due to poor bonding between rubber and cement matrix. This research aims to evaluate the mechanical and thermal properties of rubberised concrete produced by using different proportions of rubber powder and silica fume. Ordinary Portland cement was partially replaced with silica fume by amounts of 5%, 10%, 15% and 20%, while sand was replaced by 10%, 20% and 30% with waste rubber powder. Tests were carried out in order to determine workability, density, compressive strength, splitting tensile strength, elastic modulus, thermal properties, water absorption and shrinkage of rubberised concrete. The compressive strength and splitting tensile strength of concrete produced using waste rubber powder were reduced by 10-52% and 9-57%, respectively. However, the reduction in modulus of elasticity was 2-36%, less severe than compressive and splitting tensile strengths. An optimum silica fume content of 15% was observed based on the results of mechanical properties. The average shrinkage of concrete containing 15% silica fume increased from -0.051% to -0.085% at 28 days, as the content of waste rubber powder increased from 10% to 30%. While the thermal conductivity of rubberised concrete was reduced by 9-35% compared to the control sample. Linear equations were found to correlate the density, splitting tensile strength, modulus of elasticity and thermal conductivity of concrete with silica fume and waste rubber powder.
Fruit wastes constituting up to half of total fruit weight represent a large pool of untapped resources for isolation of starch with diverse applications. In this work, the possibility of isolating starch from tropical fruit wastes and its extended application as a natural coagulant was elucidated. Amongst the 12 various parts of fruit wastes selected, only jackfruit seeds contained more than 50% of total starch content. Using alkaline extraction procedures, starch has been successfully isolated from local jackfruit seeds with a yield of approximately 18%. Bell-shaped starch granules were observed under SEM with a granule size ranging from 1.1 to 41.6 μm. Detailed starch characteristics were performed to provide a comparison between the isolated seed starch and also conventional starches. Among them, chemical properties such as the content of starch, amylose, amylopectin and the corresponding molecular weights are some of the key characteristics which governed their performance as natural coagulants. The potential use of isolated seed starch as an aid was then demonstrated in both suspensions of kaolin (model synthetic system) and Chlorella sp. microalga (real-time application) with plausible outcomes. At optimized starch dosage of 60 mg/L, the overall turbidity removal in kaolin was enhanced by at least 25% at a fixed alum dosage of 2.1 mg/L. Positive turbidity and COD removals were also observed in the treatment of Chlorella suspensions. Starches which served as bridging agents aided in the linkage of neighbouring microflocs and subsequently, forming macroflocs through a secondary coagulation mechanism: adsorption and bridging.