The economic factor of the microalgae harvesting step acts as a barrier to scaling up microalgae-based technology designed for wastewater treatment. In view of that, this study presents an alternative microalgae-bacteria system, which is proposed for eliminating the economic obstacle. Instead of the microalgae-bacteria (activated algae) flocs, the study aimed to develop activated algae granules comprising the microalgae Chlorella sp. as a target species. The presence of the filamentous microalgae (Phormidium sp.) was necessary for the occurrence of the granulation processes. A progressive decrease in frequency of the free Chlorella sp. cells was achieved once with the development of the activated algae granules as a result of the target microalgae being captured in the dense and tangled network of filaments. The mature activated algae granules ranged between 600 and 2,000 µm, and were characterized by a compact structure and significant settling ability (21.6 ± 0.9 m/h). In relation to the main aim of this study, a microalgae recovery efficiency of higher than 99% was achieved only by fast sedimentation of the granules; this performance highlighted the viability of the granular activated algae system for sustaining a microalgae harvesting procedure with neither cost nor energy inputs.
The study used activated algae granules for low-strength wastewater treatment in sequential batch mode. Each treatment cycle was conducted within 24 h in a bioreactor exposed to 235 μmol/m²/s light intensity. Wastewater treatment was performed mostly in aerobic conditions, oxygen being provided by microalgae. High removal efficiency of chemical oxygen demand (COD) was achieved (86-98%) in the first hours of the reaction phase, during which the indicator's removal rate was 17.4 ± 3.9 mg O₂/g h; NH(4)(+) was removed during organic matter degradation processes with a rate of 1.8 ± 0.6 mg/g h. After almost complete COD removal, the (O⁺) remaining in the liquor was removed through nitrification processes promoted by the increase of the liquor's oxygen saturation (O₂%), the transformation rate of NH4(+) into NO(3)(-) increasing from 0.14 ± 0.05 to 1.5 ± 0.4 mg NH4(+)/g h, along with an O₂% increase. A wide removal efficiency was achieved in the case of PO(4)(3)(-) (11-85%), with the indicator's removal rate being 1.3 ± 0.7 mg/g h. In the provided optimum conditions, the occurrence of the denitrifying activity was also noticed. A large pH variation was registered (5-8.5) during treatment cycles. The granular activated algae system proved to be a promising alternative for wastewater treatment as it also sustains cost-efficient microalgae harvesting, with microalgae recovery efficiency ranging between 99.85 and 99.99% after granules settling with a velocity of 19 ± 3.6 m/h.
The focus of this study was to assess the treatment performance and granule progression over time within a continuous flow reactor. A continuous flow airlift reactor was seeded with aerobic granules from a laboratory scale sequencing batch reactor (SBR) and fed with dairy wastewater. Stereomicroscopic investigations showed that the granules maintained their integrity during the experimental period. Laser diffraction investigation showed proof of new granules formation with 100-500 μm diameter after only 2 weeks of operation. The treatment performances were satisfactory and more or less similar to the ones obtained from the SBR. Thus, removal efficiencies of 81-93% and 85-94% were observed for chemical oxygen demand and biological oxygen demand, respectively. The N-NH(+)(4) was nitrified with removal efficiencies of 83-99% while the nitrate produced was simultaneously denitrified - highest nitrate concentration determined in the effluent was 4.2 mg/L. The removal efficiency of total nitrogen was between 52 and 80% depending on influent nitrogen load (39.3-76.2 mg/L). Phosphate removal efficiencies ranged between 65 and above 99% depending on the influent phosphate concentration, which varied between 11.2 and 28.3 mg/L.
A microalgae-bacteria system was used for dairy industry wastewater treatment in sequenced batch mode in a photobioreactor. The research investigated the influence of two light intensities: 360 and 820 μmol m(-2)s(-1) on treatment performances, microalgal cell recovery and dynamics of the protozoan community. Results showed that the light intensity of 360 μmol m(-2)s(-1) was found to be insufficient to support photosynthetic activity after the increase of bacterial biomass leading to the decrease of organic matter and ammonium removal efficiencies from 95 to 78% and 95 to 41%, respectively. Maximum microalgal cells recovery was about 63%. Continuous modification in the protozoan community was also noticed during this test. Increasing the light intensity to 820 μmol m(-2)s(-1) led to better microalgal cells recovery (up to 88%) and improved treatment performances. However, the decrease of protozoan richness to small flagellates and free-swimming ciliates was noticed. Moreover, the developed protozoan trophic network was found to be different from that identified in the conventional activated sludge system. The study emphasized that high increase of bacterial biomass promoted in nutrient- and organic matter-rich wastewater can strongly affect the treatment performances as a result of the shadow effect produced on the photoautotrophic microalgae aggregates.
The balance between biotechnological useful microorganisms species, as well as the aerobic sludge granules morphology influences the treatment plant performance. This paper presents an attempt to correlate the experimental results on wastewater treatment performance with aerobic granular sludge structural community. The experiments were conducted in two lab scale bioreactors operated in parallel at different retention times. Treatment performances achieved in both systems lead to an effluent that complies NTPA001 limits, both systems being able of simultaneous nitrification / denitrification and phosphorus removal. For qualitative and quantitative analysis of aerobic granular sludge specific microorganisms, DNA has been succeesfully isolated and purifyied from sludge samples, thus obtaining bacterial DNA extracts in concentrations of up to 56 ng/mL and 78% purity. The resulted DNA extracts were used for qPCR amplification. Amplification was carried out in the presence of a series of 10 pairs of primers for the detection / quantification of specific bacteria and genes involved in the treatment process: universal bacteria; Micotrix parvicella; Ammonia oxidizing archaea; Ammonium monooxigenase; Nitrobacter Sp.; nitrite reductase; N2O reductase; phosphorus accumulating microorganisms. The experimental results showed a qualitative and quantitative improvement of the sludge quality in terms of species distribution and share of biotechnologically useful bacteria.
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