Leachates from landfills are highly polluted with a considerable content of organic and inorganic pollutants which pose severe deterioration to environment including soil, groundwater, surface water and air. Several mitigative measures have been applied for effective management of leachate such as biological treatment, engineering device control leachate migration, physical/chemical treatment, and membrane technology. Among the alternatives, anaerobic digestion (AD) is promising, with effective removal of pollutants and high potential for renewable energy production and nutrient recovery. Landfill leachate (LFL) is an excellent source as a substrate in an AD system, with its high content of organic matters. The advantages and disadvantages of AD of LFL were extensively discussed in this review in terms of its potential as a co-substrate, pre-treatment application, and the types and design parameters of the digester. The review critically evaluated the previous studies on leachate treatment using an AD system as well as potential factors which can enhance the treatment efficiency, including the application of an integrated system, additive substances as well as potential inhibition factors. Pre-treatment methods have the potential to meet desired effluent quality of LFL before discharging into receiving bodies. The review also highlighted the application of kinetic modelling and machine learning practices, along with the potential of energy generation in AD of LFL. Additionally, the review explored the various strategies, and recent advances in the anaerobic treatment of LFL, which suggested that there is a requirement to further improve the system, configuration and functioning as a precursor in selecting suitable integrated LFL-treatment technology.

Bioflocculants can be used for cost-effective harvesting of microalgae biomass on an industrial scale. This study investigates the flocculation-based harvesting approach to recovering Chlorella vulgaris microalgae biomass using chitosan biopolymer. Response surface methodology (RSM) was used to design the experiments and optimize the critical operating parameters. Box-Behnken Design (BBD) was employed at three levels, and 17 experimental runs were conducted to determine the optimal conditions and the relationship between operating parameters. The highest biomass recovery of 99.10% was achieved at the following optimized conditions: pH of 5, flocculation time of 45 min, and chitosan concentration of 10 mg/L. Both experimental results and model outputs indicated that pH significantly impacts microalgae harvesting and that process performance is less dependent on chitosan concentration and flocculation time. The quadratic model has shown the best fit with the experimental results. The results could be applied to large-scale microalgae harvesting applications to promote microalgae biomass recovery and reduce operating costs.