The photo-Fenton oxidation treatment combined with a coagulation/flocculation process was investigated for removal of chemical oxygen demand (COD) from a refractory petroleum refinery wastewater. Scrap iron shavings were used as the catalyst source. A response surface methodology (RSM) with a cubic IV optimal design was employed for optimizing the treatment process. Kinetic studies showed that the proposed process could be described by a two-stage, second-order reaction model. Experiments showed that precipitation of iron ions can be utilized as a post-oxidation coagulation stage to improve the overall treatment efficiency. More than 96.9% of the COD removal was achieved under optimal conditions, with a post-oxidation coagulation stage accounting for about 30% of the removal, thus confirming the collaborative role of oxidation and coagulation in the overall treatment. A low-velocity gradient of 8.0 s⁻¹ for a short mixing time of 10 min resulted in optimum post-oxidation coagulation. Comparison of photo-Fenton oxidation to a standard Fenton reaction in the same wastewater showed more rapid COD removal for photo-Fenton, with an initial second-order rate constant of 4.0 × 10⁻⁴ L mg⁻¹ min⁻¹ compared to the Fenton reaction’s overall second-order rate constant of 7.0 × 10⁻⁵ L mg⁻¹ min⁻¹.

Growing rice with less water is direly needed due to declining water sources worldwide, but using methods that require less water inputs can have an impact on grain characteristics and recovery. A 2-year field study was conducted to evaluate the impact of conventionally sown flooded rice and low-water-input rice systems on the grain characteristics and recovery of fine rice. Three fine grain rice cultivars—Super Basmati, Basmati 2000, and Shaheen Basmati—were grown under conventional flooded transplanted rice (CFTR), alternate wetting and drying (AWD), and aerobic rice systems. Grain characteristics and rice recovery were significantly influenced by different water regimes (production systems). Poor milling, including the lowest percentage of brown (head) rice (65.3%) and polished (white) rice (64.2–66.9%) and the highest percentage of broken brown rice (10.2%), husk (24.5%–26.3%), polished broken rice (24.7%), and bran (11.0–12.5%), were recorded in the aerobic rice system sown with Shaheen Basmati. With a few exceptions, cultivars sown in CFTR were found to possess a higher percentage of brown (head) and polished (white) rice and they had incurred the least losses in the form of brown broken rice, husk, polished broken rice, and bran. In conclusion, better grain quality and recovery of rice can be attained by growing Super Basmati under the CFTR system. Growing Shaheen Basmati under low-water-input systems, the aerobic rice system in particular, resulted in poor grain characteristics tied with less rice recovery.

In the present study, the performance of three selected aquatic plants [Hydrilla verticillata (H), Ceratophyllum demersum (C), and Lemna minor (L)] was evaluated for As removal from water when used in a successive application approach. The plants were subjected to 4 L of As-containing Hoagland medium (500 and 2500 μg L⁻¹ as low and high exposure, respectively) for a period of 21 days in slots of 7 days each. The results showed that total As removal in 21 days varied in different combinations. The best combination was HCL showing 27 and 18% As removal in low and high As treatments, respectively, followed by HLC (21 and 16%), and LCH (15% and 12%). The lowest As removal was achieved by LHC and CLH combination in low As treatment (11%) and by CLH in high As treatment (6%). Individual plant exhibited different removal potential from combination to combination and from application at various stages. The contribution of Hydrilla varied from 8 to 52%, Ceratophyllum from 18 to 64% and Lemna from 18 to 66%. The study advocates the combination of Hydrilla-Ceratophyllum-Lemna for achieving the maximum As removal in the same period.

Different from direct application of free nanoparticles (NPs) in water treatment, a composite material is used to reduce the release and potential toxic effects of NPs with maintained adsorption capacity and kinetics. Novel monolithic composites with TiO₂ NPs incorporated into the walls of macroporous cryogels were synthesized and evaluated for material characteristics and their efficiency for removal of Pb(II) from aqueous solution in batch test and continuous mode. The uniformly distributed 6% TiO₂-cryogel is shown to be optimal for minimizing TiO₂ NP losses while maximizing Pb(II) removal. Under (25.0 ± 0.1) °C with the initial Pb(II) concentration of 10 mg/l, TiO₂-cryogels exhibit excellent adsorption characteristic for Pb(II) removal with adsorption capacity up to 23.27 mg/g TiO₂, which is even a little higher than that of TiO₂ NPs (21.58 mg/g TiO₂), and the results fit well with Langmuir–Freundlich isotherm. Both adsorbents work well in higher pH range with the highest removal rate at pH 6 for TiO₂-cryogel, and the adsorption mechanism might be strong chemical interaction. Pseudo-second-order process can better describe the adsorption process rather than pseudo-first-order for both adsorbents. The external mass transfer process of Pb(II) on TiO₂ NPs is much faster than that on TiO₂-cryogel, and the ultimate equilibrium time is about the same (3 h) on both adsorbents. The synthesized composites could also withstand a continuous treatment, and the effect of competing and co-existing constituents such as Cd²⁺, SO₄²⁻ and dissolved organic matter (DOM) is almost negligible. The composite design with small particles embedded into cryogels is proved to successfully keep the adsorption activity of TiO₂ NPs and prevent them from releasing into the environment in engineering practice.

Hexavalent chromium (Cr(VI)) and dyes are of particular environmental concern and need to be removed from water urgently due to their high toxicity. Herein, we explored the possibility of electron transferring from dye Orange II (OII) to Cr(VI) under UV and simulated solar light irradiation, expecting to simultaneously decolorize dyes and reduce Cr(VI). Experimental results show that light irradiation can partially decolorize OII but has no ability to reduce Cr(VI) in solution only with OII or Cr(VI). However, both dyes and Cr(VI) can effectively and simultaneously be decolorized and reduced in the solution containing both OII and Cr(VI) under light irradiation, and a low pH level and high OII/Cr(VI) concentration ratio significantly favor the co-removal. Additionally, insoluble organo–Cr(III) complexes identified by FTIR and XPS characterization were generated during the reaction. These complexes are beneficial to the removal of chromium and total organic carbon from water. The possible degradation pathway of OII is further proposed based on the detection of degraded products by GC-MS analysis. The results of this work offer an approach for simultaneously removing multiple contaminants.

Aeration of the biological reactor in wastewater treatment plants (WWTPs) represents one of the major cost items, which may account for more than 50% of the total energy consumption. Therefore, airflow rate must be supplied based on the real needs of the biological reactions and the goals to be achieved in terms of removal efficiency and effluent quality. Among the different strategies available to optimize energy consumption of air supply, the Oxy Fuzzy logic and oxidation reduction potential (ORP)-based control systems have proven to be efficient and reliable. The present study compares the effects of these two control systems in terms of energy consumption and efficiency of COD and ammonia oxidation in the activated sludge reactors of two WWTPs for domestic sewage. Both systems allowed to largely comply with the limits set on the effluent for COD and ammonia in spite of the dynamic pattern of the influent load. The Oxy Fuzzy system led to reducing energy consumption by 13% while the ORP control system only by 2%, as average per year. The Oxy Fuzzy system showed higher flexibility, being more capable of adapting the set-points in relation to the influent load. The ORP system seemed to be more suitable for plants where the influent load does not change significantly: the set-points are fixed and the input load can be properly managed only for limited variations.

This study describes the effect of microwave and low-frequency ultrasonic pretreatment power intensity, time and density on thickened excess activated sludge (TEAS) characteristics and anaerobic digester performance. Key parameters affecting the efficiency of ultrasonic and microwave pretreatment were identified and optimised. The effect of change in ultrasonication and microwave pretreatment conditions on sludge degradation and other characteristics were analysed. Ultrasonication power, density and time were important factors in the sludge solubilisation process. Microwave density and pretreatment time also influenced solubilisation of TEAS, and the effects were investigated for treatment densities of 3.2, 4.6 and 6.4 W/ml and treatment duration of 1–7 min. Higher sludge degradability, higher volatile solid removal and better digester performance were achieved for anaerobic digestion with lower ultrasonication power of 80 W, ultrasonication time of 6 min, and ultrasonic density of 0.32 W/ml. The volume of biogas produced and kinetics, dewaterability of digested sludge, COD reduction and other sludge properties were optimised for the aforementioned ultrasonication and microwave pretreatment conditions for TEAS. It was observed that sludge dewaterability deteriorated with increasing sonication power density and sludge solubilisation. Hence, the balance between sludge dewaterability and solubilisation should be maintained for optimum performance. Thus, the selection of ultrasonic pretreatment time and power is a trade-off between sludge solubilisation and dewaterability.

Acute (24 h) and sublethal (35 days) effects of cadmium chloride (CdCl₂) were examined in Cirrhinus mrigala using various endpoints (accumulation pattern, thyroid hormones (THs), and antioxidants). The mean concentrations of CdCl₂ for 24 and 96 h were found to be 35.974 and 22.387 mg L⁻ˡ, respectively. LC50 concentration of CdCl₂ for 24 h (35.97 mg L⁻ˡ) was used for the acute study. For the sublethal studies, fish were exposed to 3.59 mg L⁻¹ (Treatment I) and 7.19 mg L⁻¹ (Treatment II) corresponding to 1/10th and 1/5th of 24 h LC50 of the CdCl₂. During acute exposure, higher accumulation of CdCl₂ was noticed in the gill, liver, and kidney of C. mrigala, which is found in the order gill > liver > kidney tissues. Similarly, in sublethal treatments (Treatment I and II), a concentration and time-dependent increase of CdCl₂ accumulation was noticed in the order of gill > liver > kidney. GSH, GST, and GPx activities were found to be relatively lower from the treated groups in both acute and sublethal treatments. However, LPO activity was significantly increased in CdCl₂-treated fish C. mrigala. Further, plasma T₃ reduction was more pronounced than T₄ in acute study. During sublethal treatments, both T₄ and T₃ levels showed a continuous decrease as the exposure period extended. All the values in this study were statically significant (P < 0.01 and P < 0.05).

Plants of the urban environment are exposed to a wide range of pollutants, including heavy metals. This research studies in situ the eco-physiological and antioxidant responses of holm oak (Q. ilex) leaves to Pb and Cd to assess the mechanisms of metal tolerance in this species, widely used as biomonitor. Leaves of plants grown at parks and roadsides were analyzed for photosynthetic activity, Pb and Cd concentration in tissues and cell-free extracts, thiol groups, D1 and Rubisco protein content, ascorbic acid (AsA) amount, and catalase (CAT) activity. The main results evidenced that Cd concentration was higher in leaves collected at the park out from the downtown; whereas Pb was most abundant in leaves sampled at the roadside nearby the highway. Pb in cell-free extracts was higher in park than in roadside leaves. Although Cd in the leaf tissues was twofold lower than Pb, it was more abundant than Pb in cellular extracts deprived of all particulate matter. Leaves responded to different concentration of Cd and Pb modulating some eco-physiological and biochemical traits, roadside leaves showed reduced leaf lamina, higher content of photosynthetic pigments, hydrogen peroxide, and AsA, as well as higher CAT activity compared to park leaves. In the roadside leaves, a stress condition for photosynthetic apparatus can be hypothesized on the basis of the decline of photochemical activity, the increase of NPQ, and the reduction of Rubisco and D1 protein content. The elevated presence of thiol groups in these leaves suggests a possible role of Pb and Cd in activation of antioxidant responses.

Forest fire is a natural disturbance that occurs in many terrestrial ecosystems specifically in the semi-arid environments and is considered to be an important cause of environmental change. Though many causes of fire are identified, including lightning, volcanic eruption, power line sparks, etc., human involvement is the most significant factor. Fire events are able to alter the physical, chemical and biogeochemical properties of the soil and surface materials and are able to release major and trace metals into the environment. This may be more significant in mining-affected and industrial landscapes, where elevated concentrations of metals present in the soil. After the fire event, metals become more mobile due to the increase in soil surface exposure and the mobility associated with ash dispersal. This mobility may increase the bioavailability of the metals, which may generate water quality issues and may contribute to human and environmental health concerns. Even though, the influences of fire on many soil properties are well established, the behaviour of metals with respect to fire is not well investigated. However, a few studies report that major and trace metals include Cd, Cr, Co, Cu, Hg, Mn, Ni, Pb, Zn and As are mobilized after fire with increased concentrations in soil and water resources and this might pose a risk to human health and ecosystems. Climate change may increase the intensity, frequency and areal extend of fire events and hence increase the metal concentrations and their potential health impacts. This paper reviews post-fire (wild fire) mobility of metals in soil common in contaminated forest ecosystems. The human and ecological health risks of these metals are also considered.