Potential of biogenic and non-biogenic waste materials as flocculant for algal biomass harvesting: Mechanism, parameters, challenges and future prospects

Evaluation of the actinia-shaped composite coagulant for removal of algae in water: Role of charge density

A series of novel cationic modified actinia-shaped composite coagulant (AMS-C), with similar tentacle length and distribution but different charge density (CD), was successfully designed and fabricated by combination of a cationic graft starch and attapulgite (ATP). AMS-C shows a high efficiency in coagulative removal of Microcystis aeruginosa from water over a wide pH range. The algae-harvesting efficiency of optimized AMS-C can reach to 92.27 % only within 1.0 min after settlement and its maximal harvesting efficiency is as high as 99.25 % at the optimum dosage of 1.5 mg/L. This can be attributed to its special composited structure with abundant cationic long tentacle chains. CD of AMS-C is a key structural factor. AMS-C with a relatively high CD obviously enhanced the coagulation efficiency and settling performance through the improved charge neutralization, besides, the distinct long tentacle chains of AMS-C allowed its easy accessibility and tightly contacted with the algal cells, and thus facilitated the formation of large, dense and fast regrowing algal flocs by the enhanced bridging and sweeping effects. The aforementioned effects were together contributed to the effective removal of algae. The effective interactions between microalga cells and the composite coagulants were also verified using extended Deryaguin-Landau-Verwey-Overbeek theory. Moreover, AMS-C was able to remove Microcystins-LR without destroying the cells, and still maintained a high algae-harvesting efficiency in real water bodies. Therefore, AMS-C, with the advantages of high-performance, environmentally-friendliness and low-cost, has notably promising application prospects in effective treatment of harmful algal blooms.

Upcycling harmful algal blooms into short-chain organic matters assisted with cellulose-based flocculant

Upcycling harmful algal blooms (HABs) into short-chain organic matters (SCOMs) presents a significantly underexplored opportunity for addressing environmental concerns and achieving circular economy. But there are challenges of low HABs harvesting and SCOMs conversion efficiencies. To address these issues, a novel cellulose-based flocculant derived from abundant agricultural waste (wheat straw) was developed. This flocculant possesses high surface positive charge to aggregate negatively charged microalgae cells via charge neutralization mechanism, resulting in HABs harvesting efficiency of 97 %. Moreover, the flocculant can serve as a carbon to nitrogen (C/N) regulator to optimize the harvested slurry properties for downstream fermentation. Following hydrothermal pretreatment for one hour, the HABs-flocculant slurry was effectively converted into SCOMs with a total energy output of 64.3 kJ/L and energy conversion efficiency of 67 %, in which SCOMs was major contributor (92 %). This work may inspire eco-friendly and cost-effective approach for HABs disposal with extra benefits of SCOMs production.

Technologies for harvesting the microalgae for industrial applications: Current trends and perspectives

Microalgae are emerging as a promising source for augmenting the supply of essential products to meet global demands in an environmentally sustainable manner. Despite the potential benefits of microalgae in industry, the high energy consumption for harvesting remains a significant obstacle. This review offers a comprehensive overview of microalgae harvesting technologies and their industrial applications, with particular emphasis on the latest advances in flocculation techniques. These cutting-edge methods have been applied to biodiesel production, food and nutraceutical processing, and wastewater treatment. Large-scale harvesting is still severely impeded by the high cost despite progress has been made in laboratory studies. In the future, cost-effective microalgal harvesting will rely on efficient resource utilization, including the use of waste materials and the reuse of media and flocculants. Additionally, precise regulation of biological metabolism will be necessary to overcome algal species-related limitations through the development of extracellular polymeric substance-induced flocculation technology.