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.

This paper emphasized the influence of the main operating parameters of ultrasonic biological sludge pretreatment onto disintegration (DD-COD) and solubilizing degree of organic matter content. The optimal ultrasonic reaction time, energy and amplitude of ultrasonic waves and pH of the sludge (non-modified pH and pH 8.5) were established taking into account their influence on the solubility level of COD, an evolution of particles size. Correlations between disintegration degree and dimensional analysis were performed. Ultrasonic reactor operating to 20 kHz ultrasound frequency was a close system having cooling water jacket. Experimental tests in different operating conditions (reaction time 5 � 60 min., ultrasound energy 2000 � 9000 kJ, pH = 6.5/8.5) demonstrated that alkaline ultrasonic treatment (pH = 8.5, initial homogeneous COD = 72600 mg O2/L) at medium - high ultrasound energy levels led to highest disintegration degree � DD 12% (comparing with pH = 6.5 � DD ~ 5%). Still, the process should be managed carefully because of possibility to have important variation of DD during the ultrasonic treatment.

A sol–gel synthesis technique was employed for the preparation of anatase phase {001}-TiO2/Au hybrid nanocomposites (NCs). The scalable, schematic, and cost-efficient method was successfully modified using HF and NH4OH capping agents. The photocatalytic activity of the as-synthesized {001}-TiO2/Au NCs were tested over 2-cycle degradation of methylene blue (MB) dye and pharmaceutical active compounds (PhACs) of ibuprofen and naproxen under direct sunlight illumination at 35 °C and 44,000 lx. Transmission electron microscopy (TEM), high resolution transmission electron microscopy (HR-TEM), fast Fourier transform (FFT), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS), and ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis DRS) were employed for the characterization of the as-prepared sample. The characterization results from the TEM, XPS, and XRD studies established both the distribution of Au colloids on the surface of TiO2 material, and the presence of the highly crystalline structure of anatase {001}-TiO2/Au NCs. Photodegradation results from the visible light irradiation of MB indicate an enhanced photocatalytic performance of Au/TiO2 NCs over TiO2. The results from the photocatalytic activity test performed under direct sunlight exposure exhibited promising photodegradation efficiencies. In the first cycle, the sol–gel synthesized material exhibited relatively better efficiencies (91%) with the MB dye and ibuprofen, while the highest degradation efficiency for the second cycle was 79% for the MB dye. Pseudo first-order photodegradation rates from the first cycle were determined to be comparatively slower than those from the second degradation cycle.

Ultrasonic treatment has become a modern method for removal of micropollutants and refractory compounds from water/wastewater and to improve biodegradation efficiency of biological activated sludge from wastewater treatment plants, in order to produce biogas. This paper is referring to the ultrasonic pretreatment of biological activated sludge, before anaerobic fermentation phase, to increase the amount of biogas generation. The pretreatment of biological sludge is based on two steps: alkaline digestion and ultrasonication. Ten minutes of alkaline condition (pH 9.5 - 10.5) followed by 10 minutes ultrasonication (20 kHz frequency) were the general operating condition of sludge pretreatment phase. Parallel tests (with and without ultrasonic pretreatment step) were performed in order to assess the effect of ultrasonic pretreatment on biogas generation. Ultrasonication in alkaline condition of biological sludge heave led to doubling the amount of biogas generated in anaerobic fermentation phase.

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