A dual-growth-limited continuous operated bioreactor (chemostat) was used to enhance lipid accumulation in an enrichment culture of microalgae. The light intensity and nitrogen concentration where both limiting factors resulting in high lipid accumulation in the mixed culture. Both conditions of light and nitrogen excess and deficiency were tested. Strategies to selectively enrich for a phototrophic lipid-storing community, based on the use of different nitrogen sources (ammonium vs. nitrate) and vitamin B supplementation in the growth medium, were evaluated. The dual limitation of both nitrogen and light enhanced the accumulation of storage compounds. Ammoniacal nitrogen was the preferred nitrogen source. Vitamin B supplementation led to a doubling of the lipid productivity. The availability of vitamins played a key role in selecting an efficient lipid-storing community, primarily consisting of Trebouxiophyceae (with an 82 % relative abundance among eukaryotic microorganisms). The obtained lipid volumetric productivity (387 mg L⁻¹ d⁻¹) was among the highest reported in literature for microalgae bioreactors. Lipid production by the microalgae enrichment surpassed the efficiencies reported for continuous microalgae pure cultures, highlighting the benefits of mixed-culture photo-biotechnologies for fuels and food ingredients in the circular economy.

The European Union's Environmental Technology Verification (ETV) program aims to foster innovative environmental technologies to reach the market and reassure potential users. This paper presents an investigation of using ETV for three technologies, being developed within the EU Zero Brine research and innovation project. The technologies were designed to recover high quality water, salts and minerals from brine solutions. The technologies in focus are the forward feed MED evaporator, the Multi Feed - Plug Flow Reactor Crystalliser and Eutectic Freeze Crystallization. The study sought to understand the challenges of the ETV process, the readiness and eligibility of technologies, and possible preparations within the project lifetime. Challenges identified included: understanding what sufficient market readiness is, and achieving this within the duration of a project (also linked to funding allocation for the ETV process); and developing suitable performance claims, supported with sufficient levels of test data. A simple framework is presented to aid the integration of ETV into the development process. It promotes the use of life cycle assessment to understand the environmental added value of the technology and aid the development of performance claims.

Mixed-culture biotechnologies are widely used to capture nutrients from wastewater. Purple non-sulfur bacteria (PNSB), a guild of anoxygenic photomixotrophic organisms, rise interest for their ability to directly assimilate nutrients in the biomass. One challenge targets the aggregation and accumulation of PNSB biomass to separate it from the treated water. Our aim was to enrich and produce a concentrated, fast-settling PNSB biomass with high nutrient removal capacity in a 1.5-L, stirred-tank, anaerobic sequencing-batch photobioreactor (SBR). PNSB were rapidly enriched after inoculation with activated sludge at 0.1 gVSS L^–1 in a first batch of 24 h under continuous irradiance of infrared (IR) light (>700 nm) at 375 W m^–2, with Rhodobacter reaching 54% of amplicon sequencing read counts. SBR operations with decreasing hydraulic retention times (48 to 16 h, i.e., 1–3 cycles d^–1) and increasing volumetric organic loading rates (0.2–1.3 kg COD d^–1 m^–3) stimulated biomass aggregation, settling, and accumulation in the system, reaching as high as 3.8 g VSS L^–1. The sludge retention time (SRT) increased freely from 2.5 to 11 days. Acetate, ammonium, and orthophosphate were removed up to 96% at a rate of 1.1 kg COD d^–1 m^–3, 77% at 113 g N d^–1 m^–3, and 73% at 15 g P d^–1 m^–3, respectively, with COD:N:P assimilation ratio of 100:6.7:0.9 m/m/m. SBR regime shifts sequentially selected for Rhodobacter (90%) under shorter SRT and non-limiting concentration of acetate during reaction phases, for Rhodopseudomonas (70%) under longer SRT and acetate limitation during reaction, and Blastochloris (10%) under higher biomass concentrations, underlying competition for substrate and photons in the PNSB guild. With SBR operations we produced a fast-settling biomass, highly (>90%) enriched in PNSB. A high nutrient removal was achieved by biomass assimilation, reaching the European nutrient discharge limits. We opened further insights on the microbial ecology of PNSB-based processes for water resource recovery.

The dewatering of algal culture requires coagulation of the algal cells. However, the coagulation in a continuous operation is slowed down through the excretion of Soluble Algal Products (SAPs). Electrocoagulation (EC), already utilized as a coagulation technique, has been investigated for its effects on SAPs characterizations. A mixed culture of Chlorella vulgaris, Scenedesmus Obliquus, Botryococcus braunii, Botryococcus sudeticus, and Afrocarpus falcatus was prepared and SAPs characteristics, including Specific Ultra Violet Absorbance (SUVA), Zeta potential, Molecular Weight (MW) fractionation, Dissolved Organic Carbon (DOC), protein and carbohydrate content, Excitation-Emission Matrix, and hydrophobicity using XAD resins, were measured and evaluated before and after electrocoagulation using mild steel and aluminum electrodes at 5 and 10 min. The results showed several improvements after EC. According to results, EC can render SAPs hydrophobicity up to 95 %, and the fluorescence peak results showed the complete removal of humic-like. Moreover, the SAPs were removed up to 21, 60, and 47 % for protein, carbohydrate and DOC, respectively. Results collectively showed that electrocoagulation might be able to mitigate the negative effects of growth on flocculation.

In this study, electrocoagulation was evaluated for landfill leachate as a complex wastewater. Effects of all significant parameters including inter-electrode gap, current density, electrode material, time, pH, electrode numbers, salinity, and concentration were investigated. This study reports the changing patterns for chemical xxygen demand (COD) removal, temperature, voltage, and pH during EC for both Fe and Al electrodes under different conditions. According to the results, the best COD removals were achieved at shortest inter-electrode distance (0.5 cm), highest current density (1000 A m⁻²), highest number of electrodes (6 plates), longest time (60 min), and within acidic pH. Furthermore, for different NaCl concentrations (0–16 g l⁻¹), both falling and rising patterns were observed. This study also provides separate results for the effect of operational parameters on pH, voltage, temperature, and energy consumption during EC. With higher inter-electrode distances, voltage and temperature rose to larger values, whereas pH fell. Besides, increases in initial pH caused rises in all voltage, temperature and pH parameters during EC. Experiments also displayed that higher values of voltage, temperature, and pH occurred at larger current densities. Additionally, with time, pH increased to more basic measures, and voltage similarly increased. Results also reported that although addition of NaCl into medium could drop the voltage and temperature, it formed both falling and rising patterns for pH at different NaCl concentrations. Plus, according to the results, voltage, temperature, and pH all experienced rising patterns in accordance with the increase in the number of electrodes. Finally, a comparative study of energy consumption was performed to analyse the operation parametric effect.

For further applications of microalgae such as bio-products, microalgal harvesting from its culture medium (e.g. wastewater) must be studied. This becomes more essential when investigating whether or not cells can stay viable to be recycled into the system. Microalgae culture, wastewater, and a mixture of both were separately electrocoagulated at wastewater Chemical Oxygen Demand ranging 66–2700 mg.l-1 and biomass dry weights between 1 and 8 g.l-1. The mixed culture contained species of C. Vulgaris, S. Obliquus, B. Braunii, B. Sudeticus, and A. Falcatus, since mixed culture technique can reduce the expenses in industrial scales by eliminating the costly sterilization strategies necessary to avoid contamination. The mixed samples were successfully separated with the efficiencies between 44-87% and 70–80% at different Chemical Oxygen Demand and biomass dry weights, respectively. In addition, it was shown that growth elements of carbon and nitrogen, although at lower rates, were consumed confirming the viability of the cells after electrocoagulation. The consumption rates for electrocoagulated samples were smaller than non-electrocoagulated samples only by 16, 12, and 31% in carbon, nitrate and ammonium concentrations, respectively. According to the obtained results electrical separation of microalgae could effectively harvest microalgae from wastewater without affecting the viability of the biomass.

The relative performance of two biofilm-based airlift reactors using different kinds of packing materials and one fixed bed biofilm reactor with a homemade packing material of high specific area (~ 1000 m²/m³) was addressed. The bioreactors operated under ferrous iron loading rates in the range of 8–120 mol Fe(II)/m³ h. Acidithiobacillus ferrooxidans cells immobilized in the three bioreactors afforded the reactions for an extended period of 120 days of continuous operation at the dilution rates of 0.2, 0.4, 0.7, 1 and 1.2 h⁻¹. The maximum ferrous iron oxidation rates achieved in this study at a hydraulic residence time of 1.2 h were about 91, 68 and 51 mol Fe(II)/m³ h for the fixed bed, airlift1, and airlft2 bioreactors. The performance data from the fixed-bed bioreactor offered a higher potential for ferrous iron oxidation because of fast biofilm development, the formation of a thick biofilm, and lower sensitivity to shear, which enhanced the startup time of the bioreactor and the higher reactor productivity. Proper kinetic models were also presented for both the startup period and the steady-state process.