Remote sensing applications in water resources management are quite essential in watershed characterization, particularly when mega basins are under investigation. Water quality parameters help in decision making regarding the further use of water based on its quality. Water quality parameters of chlorophyll a concentration, nitrate concentration, and water turbidity were used in the current study to estimate the water quality parameters in the dam lake of Wadi Baysh, Saudi Arabia. Water quality parameters were collected daily over 2 years (2017–2018) from the water treatment station located within the dam vicinity and were correspondingly tested against remotely sensed water quality parameters. Remote sensing data were collected from Sentinel-2 sensor, European Space Agency (ESA) on a satellite temporal resolution basis. Data were pre-processed then processed to estimate the maximum chlorophyll index (MCI), green normalized difference vegetation index (GNDVI) and normalized difference turbidity index (NDTI). Zonal statistics were used to improve the regression analysis between the spatial data estimated from the remote sensing images and the nonspatial data collected from the water treatment plant. Results showed different correlation coefficients between the ground truth collected data and the corresponding indices conducted from remote sensing data. Actual chlorophyll a concentration showed high correlation with estimated MCI mean values with an R² of 0.96, actual nitrate concentration showed high correlation with the estimated GNDVI mean values with an R² of 0.94, and the actual water turbidity measurements showed high correlation with the estimated NDTI mean values with an R² of 0.94. The research findings support the use of remote sensing data of Sentinel-2 to estimate water quality parameters in arid environments.

The high-energy consumption of wastewater treatment plants (WWTPs) is a crucial issue for municipalities worldwide. Most WWTPs in Greece operate as extended aeration plants, which results in high operational costs due to high energy needs. The present study investigated the energy requirements of 17 activated sludge WWTPs in Greece, serving between 1100–56,000 inhabitants (population equivalent, PE), with average daily incoming flowrates between 300–27,300 m³/d. The daily wastewater production per inhabitant was found to lie between 0.052 m³/PE·d and 0.426 m³/PE·d, with average volume of 0.217 ± 0.114 m³/PE·d. The electric energy consumption per volume unit (E_Q (kWh/m³)) was between 0.128–2.280 kWh/m³ (average 0.903 ± 0.509 kWh/m³) following a near logarithmic descending correlation with the average incoming flowrate (Q_av) (E_Q = −0.294lnQ_av + 3.1891; R² = 0.5337). A similar relationship was found between the daily electric energy requirements for wastewater treatment per inhabitant (E_PE (kWh/PE·d)) as a function of PE, which varied from 0.041–0.407 kWh/PE·d (average 0.167 ± 0.101 kWh/PE·d)) (E_PE = −0.073ln(PE) + 0.8425; R² = 0.6989). Similarly, the daily energy cost per inhabitant (E_€/PE (€/PE·d)) as a function of PE and the electric energy cost per wastewater volume unit (E_€/V (€/m³)) as a function of average daily flow (Q_av) were found to follow near logarithmic trends (E_€/PE = −0.013ln(PE) + 0.1473; R² = 0.6388, and E_€/V = −0.052lnQ_av + 0.5151; R² = 0.6359), respectively), with E_€/PE varying between 0.005–0.073 €/PE·d (average 0.024 ± 0.019 €/PE·d) and E_€/V between 0.012–0.291 €/m³ (average 0.111 ± 0.077 €/m³). Finally, it was calculated that, in an average WWTP, the aeration process is the main energy sink, consuming about 67.2% of the total electric energy supply to the plant. The large variation of energy requirements per inlet volume unit and per inhabitant served, indicate that there is large ground for improving the performance of the WWTPs, with respect to energy consumption.

Benzene, toluene, ethylbenzene, and xylenes (BTEX) are commonly encountered pollutants. The focus of the present work is on the removal of BTEX using pilot-scale constructed wetlands (CWs). Experiment carried out in three similar pilot-scale horizontal sub-surface flow constructed wetlands with an area of 35 m² (each), two of which were planted with different macrophytes (Phragmites australis and Typha latifolia), while an unplanted one was used as control. A number of hydraulic tests were carried out using lithium bromide as tracer, to assess the hydraulic residence time. Residence time distributions for the two CWs indicated that the Typha field was characterized by a void volume fraction (porosity) of 0.16 and exhibited more ideal plug flow behavior (Pe = 29.7) compared with the Phragmites field (Pe = 26.7), which had similar porosity. The measured hydraulic residence times in the planted fields were 35.8, 36.7, and 34.1 h for Typha, Phragmites, and unplanted respectively, at wastewater flow rates equal to 1 m³/d. The observed percentage removal for BTEX ranged between 46 and 55%. The average removal in the Phragmites field was 5% higher than the Typha field and 23% higher than the unplanted field. BTEX removal was primarily attributed to volatilization; however, biodegradation also played a significant role.