Nutrients' behavior and removal in an activated sludge system receiving Olive Mill Wastewater

Current progress of continuous-flow aerobic granular sludge: A critical review

Aerobic granular sludge (AGS) is promising for water resource recovery. Despite the mature granulation strategies in sequencing batch reactor (SBR), the application of AGS-SBR in wastewater treatment is usually costly as it requires extensive infrastructure conversion (e.g., from continuous-flow reactor to SBR). In contrast, continuous-flow AGS (CAGS) that does not require such infrastructure conversion is a more cost-effective strategy to retrofit existing wastewater treatment plants (WWTPs). Formation of aerobic granules in both batch and continuous-flow mode depends on many factors, including selection pressure, feast/famine conditions, extracellular polymeric substances (EPS), and environmental conditions. Compared with AGS in SBR, creating proper conditions to facilitate granulation in continuous-flow mode is challenging. Researchers have been seeking to tackle this bottleneck by studying the impacts of selection pressure, feast/famine conditions, and operating parameters on granulation and granule stability in CAGS. This review paper summarizes the state-of-the-art knowledge regarding CAGS for wastewater treatment. Firstly, we discuss the CAGS granulation process and effective parameters (i.e., selection pressure, feast/famine conditions, hydrodynamic shear force, reactor configuration, the role of EPS, and other operating factors). Then, we evaluate CAGS performance in removing COD, nitrogen, phosphorus, emerging pollutants, and heavy metals from wastewater. Finally, the applicability of the hybrid CAGS systems is presented. At last, we suggest that integrating CAGS with other treatment methods such as membrane bioreactor (MBR) or advanced oxidation processes (AOP) can benefit the performance and stability of granules. However, future research should address unknowns including the relationship between feast/famine ratio and stability of the granules, the effectiveness of applying particle size-based selection pressure, and the CAGS performance at low temperatures.

On the modeling and optimization of two-phase olive-oil washing wastewater treatment and polyphenols recovery by ceramic tubular microfiltration membranes

This research is focused on modelling and optimization of the performance of a 'green procedure' based on microfiltration (MF) technology, for recovery of high added-value antioxidant compounds (TACs) from two-phase olive-oil washing wastewater (OOWW) and its treatment. Concern of olive oil industry to improve the production process in line with Circular Economy is vital to make it respectful with the environment including the management of the generated effluents. Key operational factors of the MF process were studied, modelled and optimized by multifactorial statistical analysis. Box-Behnken design was implemented and data analyzed by ANOVA and interpreted by RSM methodology. MF flux was ulteriorly modelled by a second-grade quadratic fitting equation comprising the significant operating variables, being them pressure and tangential velocity. Optimized flow achieved 10962.4 L/hm² at 8.5 bar, 4.2 L/min tangential velocity, ambient temperature (25 °C) and raw pH (5.13). Finally, multiple-response permitted to optimize up to 67% TSS rejection and minimum rejection of TACs of 22.9%, upon 3.57 bar, 4.2 m/s, 23.4 °C and effluent pH of 5.1, meaning the recovery of 77.1% of TACs from OOWW in the permeate stream, up to 1207.1 mg/L. Results show that the proposed process allows a reduction in energy consumption by using the raw effluent with unmodified pH and ambient temperature.