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Excessive growth of microalgae due to use of fertilizers, detergents, and discharge of domestic waste results in the eutrophication and degradation of the water quality of lakes and ponds. The present study aimed to improve the quality of pond water by harvesting mixed cultures of microalgae grown in a pond using Moringa oleifera (MO) extract as a coagulant. The study comprises evaluating the effects of coagulant dose, pH, mixing time, mixing rate, settling time, temperature, and algal biomass concentration on nutrient and microalgae cell removal. The pond water quality restoration was assessed by characterization of raw and MO-treated water. The MO was found to be very effective for mixed culture microalgae harvesting with flocculation efficiency of 92.97% at dose of 15 ml/L of MO extract, pH 8, mixing time 5 min, mixing rate 30 rpm, and 20-min settling time. The results have shown significant improvement in pond water quality with reduction in turbidity from 388.16 ± 48.23 to 8.39 ± 1.0 NTU, chlorophyll-a from 635.01 ± 86.20 to 15.03 ± 1.5 mg/m 3 , total nitrogen (TN) from 20.37 ± 4.64 to 12.10 ± 1.19 mg/L, and total phosphorus (TP) from 2.05 ± 0.10 to 1.61 ± 0.24 mg/L. PRACTITIONER POINTS: Production of biomass and water quality improvement of the pond at the same time MO extract shows better removal efficiency at a lower dose with fast kinetics Cost-effective flocculant saves time and energy during flocculation Common bioflocculant to remove both microalgae and nutrients., (© 2020 Water Environment Federation.)

Microalgae with wide range of commercial applications have attracted a lot of attention of the researchers in the last few decades. However, microalgae utilization is not economically sustainable due to high cost of harvesting. A wide range of solid - liquid separation techniques are available for microalgae harvesting. The techniques include coagulation and flocculation, flotation, centrifugation and filtration or a combination of various techniques. Despite the importance of harvesting to the economics and energy balance, there is no universal harvesting technique for microalgae. Therefore, this review focuses on assessing technical, economical and application potential of various harvesting techniques so as to allow selection of an appropriate technology for cost effectively harvesting of microalgae from their culture medium. Various harvesting and concentrating techniques of microalgae were reviewed to suggest order of suitability of the techniques for four main microalgae applications i.e biofuel, human and animal food, high valued products, and water quality restoration. For deciding the order of suitability, a comparative analysis of various harvesting techniques based on the six common criterions (i.e biomass quality, cost, biomass quantity, processing time, species specific and toxicity) has been done. Based on the order of various techniques vis-a-vis various criteria and preferred order of criteria for various applications, order of suitability of harvesting techniques for various applications has been decided. Among various harvesting techniques, coagulation and flocculation, centrifugation and filtration were found to be most suitable for considered applications. These techniques may be used alone or in combination for increasing the harvesting efficiency., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Excessive growth of microalgae results in the eutrophication and degradation of water quality in lakes and ponds. Microalgae have proved to be very beneficial for sustainable development. Its applications, starting from growth to death, make them a valuable resource for food and energy production. However, presence of microalgae in surface water sources affects water quality and its beneficial uses. The excess nutrient-rich agriculture runoff also adds problems to the downstream systems. Nutrient removal and microalgae harvesting are considered the most problematic task for improving water quality of surface waters. The main objective of the present study was to improve the water quality of nutrient rich waters using attached growth systems. The use of batch and continuous flow baffled attached growth systems has successfully improved the water quality and produced algal biomass that can be utilized or transformed into other valuable products. The performance of continuous flow baffled attached growth system was better and it improved the quality of oligotrophic, mesotrophic, eutrophic and hypereutrophic waters by removing>95% of TN and TP in 35, 63, 63 and 4 days, with biomass productivity of 2.69 ± 0.21, 3.17 ± 0.06, 3.61 ± 0.16 and 4.64 ± 0.3 gDWm−2 day−1, respectively. [ABSTRACT FROM AUTHOR]

With realizing the potential of algal biomass as a good natural resource for the harnessing of valuable bioproducts, algal biomass production has gained a lot of interest in recent years. However, due to some limitations such as low harvesting efficiency, higher nutrient supply, and high water requirement, the production of algal biomass is uneconomical. Over the past several years, researchers are continuously working on growing algae as a biofilm for easy microalgae harvesting, concentration of algal biomass to a great extent, and requiring less quantity of water as compared to other microalgae cultivation methods. Most of the documented studies have been carried out on either use of algal biomass for tertiary treatment of wastewater or cultivation and harvesting of algal biomass for biofuel production. Limited research studies have documented other applications of the algal biofilm system. The present review paper summarizes the current knowledge on various factors affecting microalgae growth, development of algal biofilm, and operation of algal biofilm systems to help properly understand and optimize these factors for better economics, more positive environmental impacts, and successful potential applications of the attached growth systems. The important factors include the structure of algal biofilms, EPS matrix, supporting materials, nutrient availability, environmental conditions, and biofilm thickness and harvesting frequency. The potential applications such as wastewater treatment, CO2 sequestration, microalgae–microbial fuel cell, large-scale biomass production, and water quality improvement are also discussed. [ABSTRACT FROM AUTHOR]