Analysis on the flocculation characteristics of algal organic matters.

Algal organic matters (AOM) produced by cyanobacteria is an important part of the organic pollution and deterioration of water quality. Due to the complex composition, high solubility and easy dispersion of AOM, its flocculation characteristics become an important factor affecting the treatment for cyanobacteria-containing water. In this study, the cyanobacteria both in the Lab- and Taihu-environment were taken as research objects, aiming at the flocculation characteristic analysis of their extracellular organic matters (EOM) and intracellular organic matters (IOM) with the release risks. Results showed that EOM required more coagulant dosage than IOM and its removal effect was relatively lower. The complex water environment factors in Taihu Lake might cause easier separation of cyanobacterial AOM, which increased the removal efficiency of EOM and IOM by 11.05-26.18% and 8.54.-12.8%, respectively. The flocculation efficiency of cyanobacterial AOM was not only affected by the zeta potential driven charge neutralization, but also by the component distribution and content of AOM. Aromatic protein-like microbial metabolites were the main combination targets of coagulants rather than humic acids and fulvic acids. The wider floc particle size range and worse floc uniformity of cyanobacterial EOM was also one of the reasons for its poor coagulation effect. This paper provides an important theoretical basis and data support for the targeted flocculation and removal of cyanobacterial AOM.

Aperfeiçoamento de modelo de estimativa da eficiência de remoção de turbidez da água em floculadores tubulares helicoidais / Model improvement for estimating of water turbidity removal efficiency in helical tubular flocculators

RESUMO Estudos científicos têm demonstrado que os floculadores tubulares helicoidais (FTHs) têm alta eficiência na formação de flocos e baixo tempo de retenção hidráulica, quando comparados aos floculadores comumente usados em tratamento de água e esgoto. No entanto, sua aplicação prática é limitada, pois ainda existe demanda significativa por avanços na compreensão da relação entre a hidrodinâmica da unidade e o processo de floculação, bem como critérios e metodologias para auxiliar em projeto racionais de FTH. Nesse contexto, este estudo teve por objetivo propor um aperfeiçoamento no modelo de estimativa de eficiência de remoção de turbidez apresentado por Oliveira (2014), o qual leva em conta um conjunto de parâmetros geométricos, hidráulicos e hidrodinâmicos relevantes ao processo de floculação nesse tipo de reator, pela incorporação de um dos parâmetros mais representativos de processos de floculação, o gradiente de pressão normal (GPp), como uma de suas variáveis independentes. O desenvolvimento do trabalho empregou dinâmica dos fluidos computacional (CFD) no estudo de 84 configurações de FTH, contemplando regimes de escoamento laminar e turbulento. Como resultado, chegou-se a uma nova versão de modelo de estimativa da eficiência de remoção de turbidez da água que, em relação à versão original: tem menor número de variáveis independentes; apresenta melhor ajuste aos dados experimentais; e é mais simples do ponto de vista operacional.

ABSTRACT Scientific studies have been demonstrating that helical tubular flocculators (HTFs) have high efficiency in floc formation and low hydraulic retention time when compared to flocculators commonly used in water and wastewater treatment. However, its practical application is still limited because there is still a significant demand for advances in the understanding of the relationship between the hydrodynamics of the unit and the flocculation process, as well as for criteria and methodologies in support to the rational design of HTF. In this context, the objective of this study was to propose an improvement in the model of turbidity removal efficiency developed by Oliveira (2014), which takes into account a set of geometric, hydraulic and hydrodynamic parameters relevant to the flocculation process in this type of reactor, by incorporating one of the most representative parameters of flocculation processes, the normal pressure gradient, as one of its independent variables. The development of the work employs computational fluid dynamics (CFD) in the study of 84 HTFs configurations, considering laminar and turbulent flow regimes. As a result, a new model version for estimating water turbidity removal's efficiency in helical tubular flocculators was obtained, which, in relation to the original version, has a smaller number of independent variables, presents better fit to the experimental data and is simpler from the operational point of view.

Synthesis of polyaluminium chloride/papermaking sludge-based organic polymer composites for removal of disperse yellow and reactive blue by flocculation.

In this study, a series of polyaluminium chloride/papermaking sludge-based organic polymer (PAC-PSBF) composites with different PAC basicity and PAC/PSBF mass ratios were prepared from papermaking sludge. The basic properties of the aforementioned composites were characterized, and their flocculation efficiencies were studied in the disperse yellow (DY) and reactive blue (RB) dye removals. The results of the flocculation experiments demonstrated that PAC-PSBF composites performed better than PAC regardless of the PAC basicity or PAC/PSBF mass ratios. The composites with low PAC basicity were effective in DY and RB dye removals. PAC-PSBF composites with the same PAC basicity but higher PAC/PSBF mass ratios exerted more satisfactory color removals and floc properties in both DY and RB dye removals. PAC-PSBF composites were more pH-independent than PAC, and the excellent flocculation efficiencies of the composites was achieved at pH 4.0 to 8.0 in DY/RB dye removals. In brief, desirable flocculation efficiencies of the PAC-PSBF composites were obtained when PAC and PSBF were appropriately combined together.

Efficiency of chitosan and eggshell on harvesting of Spirulina sp. in a bioflocculation process

Aims@#Microalgae were very small in size (a few μm) and have a low concentration in the medium. Due to their size, harvesting of microalgae from their growth medium remain a major obstacle in downstream processing. Efficient harvesting method must be applied to ensure it is cost effective, preserves quality and improves the culture process which is important for commercial algal production. Common harvesting methods use to harvest microalgae from their growth medium are centrifugation, filtration, flotation, sedimentation, and flocculation. Flocculation is a common method use to harvest microalgae due to low cost, save time and highly efficient method for algae biomass recovery. The purpose of this study was to investigate the effects chitosan and eggshell on flocculation of microalga Spirulina platensis. Chitosan and eggshell were chosen as flocculant due to their biodegradability, non-toxicity and safe to handle. @*Methodology and results@#The efficiencies of flocculation process were examined by conducting experiments over a range of culture pH, flocculant concentrations and flocculation time using chitosan and eggshell as flocculant agent. Under optimized flocculation conditions of 50 mg/L chitosan at pH 8 culture media for 90 min of flocculation time and 4 mg/mL eggshell at pH 4 culture media for 8 min of flocculation time, the maximum flocculation efficiency obtained was 79.98±1.65% and 97.17±1.38%, respectively. @*Conclusion, significance and impact of study@#Therefore, it can be concluded that chitosan and eggshell could be used as flocculants for harvesting large scale microalgal biomass production. Nevertheless, eggshell is more economical and more efficient compared to chitosan in harvesting microalgae biomass.

Environmental evaluation of flocculation efficiency in the separation of the microalgal biomass of Scenedesmus sp. cultivated in full-scale photobioreactors.

In this paper the environmental evaluation of the separation process of the microalgal biomass Scenedesmus sp. from full-scale photobioreactors was carried out at the Research and Development Nucleus for Sustainable Energy (NPDEAS), with different flocculants (iron sulfate - FeCl3, sodium hydroxide - NaOH, calcium hydroxide - Ca(OH)2 and aluminum sulphate Al2(SO4)3, by means of the life cycle assessment (LCA) methodology, using the SimaPro 7.3 software. Furthermore, the flocculation efficiency by means of optical density (OD) was also evaluated. The results indicated that FeCl3 and Al2(SO4)3 were highly effective for the recovery of microalgal biomass, greater than 95%. Though, when FeCl3 was used, there was an immediate change in color to the biomass after the orange colored salt was added, typical with the presence of iron, which may compromise the biomass use according to its purpose and Al2(SO4)3 is associated with the occurrence of Alzheimer's disease, restricting the application of biomass recovered through this process for nutritional purposes, for example. Therefore, it was observed that sodium hydroxide is an efficient flocculant, promoting recovery around 93.5% for the ideal concentration of 144 mg per liter. It had the best environmental profile among the compared flocculant agents, since it did not cause visible changes in the biomass or compromise its use and had less impact in relation to acidification, eutrophication, global warming and human toxicity, among others. Thus, the results indicate that it is important to consider both flocculation efficiency aspects and environmental impacts to identify the best flocculants on an industrial scale, to optimize the process, with lower amount of flocculant and obtain the maximum biomass recovery and decrease the impact on the extraction, production, treatment and reuse of these chemical compounds to the environment. However, more studies are needed in order to evaluate energy efficiency of the process coupled with other microalgal biomass recovery technologies. In addition, studies with natural flocculants, other polymers and changes in pH are also needed, as these are produced in a more sustainable way than synthetic organic polymers and have the potential to generate a biomass free of undesirable contaminants.

Efficient harvesting of marine Chlorella vulgaris microalgae utilizing cationic starch nanoparticles by response surface methodology.

Harvesting involves nearly thirty percent of total production cost of microalgae that needs to be done efficiently. Utilizing inexpensive and highly available biopolymer-based flocculants can be a solution for reducing the harvest costs. Herein, flocculation process of Chlorella vulgaris microalgae using cationic starch nanoparticles (CSNPs) was evaluated and optimized through the response surface methodology (RSM). pH, microalgae and CSNPs concentrations were considered as the main independent variables. Under the optimum conditions of microalgae concentration 0.75gdry weight/L, CSNPs concentration 7.1mgdry weight/L and pH 11.8, the maximum flocculation efficiency (90%) achieved. Twenty percent increase in flocculation efficiency observed with the use of CSNPs instead of the non-particulate starch which can be due to the more electrostatic interactions between the cationic nanoparticles and the microalgae. Therefore, the synthesized CSNPs can be employed as a convenient and economical flocculants for efficient harvest of Chlorella vulgaris microalgae at large scale.

Mechanistically harvesting of Chlorella vulgaris and Rhodotorula glutinis via modified montmorillonoid.

In this study, the flocculation process of Chlorella vulgaris and Rhodotorula glutinis induced by inorganic salts modified montmorillonoid was conducted. The maximum flocculation efficiency (FE) of 98.50% for C. vulgaris and 11.83% for R. glutinis were obtained with 4g/L and 5g/L flocculant within the dosage scope of 1-5g/L. The difference of FE was then thermodynamically explained by the extended DLVO theory and the FE of R. glutinis was mechanically enhanced to 90.66% with 0.06g/L cationic polyacrylamide (CPAM) at an optimum pH of 9. After that, aimed to utilize the remainder flocculant capacity, C. vulgaris culture was added to the aggregation of R. glutinis. Fortunately, the coagulation of R. glutinis and C. Vulgaris was achieved with 0.05g/L CPAM and 5g/L flocculant at pH 9 and the FE reached 90.15% and 91.24%, respectively.

Synergistic effect and mechanisms of compound bioflocculant and AlCl3 salts on enhancing Chlorella regularis harvesting.

The high energy input required for harvesting microalgae means that commercial production of microalgal biodiesel is economically unfeasible. In this study, we investigated the flocculation efficiency and synergistic mechanisms of novel coupled flocculants, AlCl3 and compound bioflocculants (CBF), to overcome this difficulty. AlCl3 flocculation was found to be very sensitive to pH, and flocculation efficiency increased from 55 to 95 % when pH increased from 4 to 10. CBF was environmental friendly, less reliant on pH, but had a relatively low flocculation of 75 % in optimum conditions. The harvesting efficiency of Chlorella regularis can achieve a satisfactory level of 96.77 % even in neutral conditions, with a CBF dosage of 0.26 g/L, AlCl3 dosage of 0.18 g/L, and coagulant aid (CaCl2) dosage of 0.12 g/L. Interestingly, compared with the use of single flocculant, the dosage of CBF, AlCl3, and coagulant aid (CaCl2) were reduced by about 52, 49, and 66 %, respectively. Besides, the aluminum (Al) ion content of the supernatant decreased significantly to a residue of only 0.03 mg/L, therefore meeting the downstream process needs easily. Patching and bridging played key roles in coupled flocculant flocculation, in which AlCl3 mainly carried out the electrical neutralization. This work provides new insight into an efficient, economical, and environmentally friendly protocol for microalgae harvesting.

Biomass production and identification of suitable harvesting technique for Chlorella sp. MJ 11/11 and Synechocystis PCC 6803.

Microalgae that can grow fast and convert solar energy into chemical energy efficiently are being considered as a promising feedstock of renewable biofuel. Mass production of microalgal oil faces a number of technical barriers that make the current production of biodiesel economically unfeasible. Small size (≈1-20 µm) and negatively charged surface of the microalgal cells pose difficulties in the process of harvesting. This leads to significant increase in the overall cost of biomass production. The present study explored different methods and conditions for harvesting of Chlorella sp. MJ 11/11 and Synechocystis PCC 6803. A customized air-lift reactor was used for the cultivation of biomass under photoautotrophic condition. Significant improvement in the rate of productivity of biomass was observed. Maximum biomass productivity of 0.25, 0.14 g L-1 d-1 for Chlorella sp. MJ 11/11 and Synechocystis PCC 6803, respectively, were obtained. Various flocculation techniques viz. auto-flocculation, inorganic, chitosan and electrolytic flocculation were used for the recovery of biomass. Among all the techniques, electro-flocculation showed high flocculation efficiency (98 %) and floatation of floc causing easy harvesting. Moreover, low-cost and easy control of the process justify electro-flocculation as a most suitable and promising technique for the recovery of microalgal cells.

Preparation and application of a novel bioflocculant by two strains of Rhizopus sp. using potato starch wastewater as nutrilite.

A complex bioflocculant MBF917 was prepared by Rhizopus sp. M9 and M17 using potato starch wastewater (PSW) as nutrilite, and its flocculation characteristics of treating PSW were studied. Culture conditions of the two strains were optimized, and flocculating conditions of the bioflocculant for treating PSW were also investigated. The optimal and economical culture conditions were determined as COD of about 1600 mg/L, 0.3 g/L urea and 0.04 g/L potassium dihydrogen phosphate, with no need of adding carbon sources or adjusting pH. When the bioflocculant was used to flocculate PSW, the optimal dosage was 0.1 mL/L with addition of 5 mL/L 10% CaCl2 as coagulant aid, and there was no need to adjust pH. After flocculation, COD and turbidity removal rates of the PSW could reach 54.09% and 92.11%, respectively, and 1.1g/L proteic substance was recycled from the PSW as a byproduct that could be used for animal feed.