The electrochemical oxidation of olive mill wastewater (OMW) over a Ti/RuO 2 anode was studied by means of cyclic voltammetry and bulk electrolysis and compared with previous results over a Ti/IrO 2 anode. Experiments were conducted at 300-1,220 mg L -1 initial chemical oxygen demand (COD) concentrations, 0.05-1.35 V versus SHE and 1.39-1.48 V versus SHE potential windows, 15-50 mA cm -2 current densities, 0-20 mM NaCl, Na 2 SO 4 , or FeCl 3 concentrations, 80°C temperature, and acidic conditions. Partial and total oxidation reactions occur with the overall rate being near first-order kinetics with respect to COD. Oxidation at 28 Ah L -1 and 50 mA cm -2 leads to quite high color and phenols removal (86 and 84%, respectively), elimination of ecotoxicity, and a satisfactory COD and total organic carbon reduction (52 and 38%, respectively). Similar performance can be achieved at the same charge (28 Ah L -1 ) using lower current densities (15 mA cm -2 ) but in the presence of various salts. For example, COD removal is less than 7% at 28 Ah L -1 in a salt-free sample, while addition of 20 mM NaCl results in 54% COD reduction. Decolorization of OMW using Ti/RuO 2 anode seems to be independent of the presence of salts in contrast with Ti/IrO 2 where addition of NaCl has a beneficial effect on decolorization.
Modern hydroponic substrates have contributed significantly to the popularity and progress of hydroponic cultivations worldwide, nevertheless, their development, transportation, and disposal often come at a significant environmental cost. Here we investigate the feasibility of partial to total replacement of conventional organic growing media constituents, such as cocodust (C), in a 20% perlite (P) and 80% cocodust substrate (hereafter control 8C), with compost from locally sourced grocery waste (W). For this purpose, four treatment mixtures were developed (6C:2W, 4C:4W, 2C:6W, 8W), with the grocery waste-compost fraction ranging from 20 to 80%, respectively (perlite constant at 20%). The new substrates were tested on hydroponic lettuce (Lactuca sativa var. Tanius) cultivation. During the 35-day experiment, lettuce physiology was evaluated using chlorophyll concentration [SPAD], chlorophyll fluorescence [Fv/Fm], number of leaves, and plant growth index. At harvest, the plant yield was evaluated using leaf area [cm2], leaf fresh and dry weight [g], as well as leaf firmness [g]. Results show that substrates with compost led to superior physiology and yield characteristics, with 8W inducing a significant increase in leaf area, chlorophyll concentration, dry weight, and firmness, by 11.6%, 5.4%, 19.8% and 12.8%, respectively, compared to the control treatment 8C. Results indicate that grocery waste-based compost is an excellent sustainable alternative for the soilless cultivation of lettuce. After its use in hydroponic cultivation, substrate material is safe to dispose of or be used as a soil amendment, thus contributing to a circular agro-food economy model.
One of the best methods for turning different types of biomass into clean energy is anaerobic digestion (AD). Organic and inorganic additives may be employed in the AD process to increase biogas output. It has been demonstrated that inorganic additives, such as micronutrients, can improve the efficiency of biogas producing reactors. These trace items can be introduced to the AD process as powders. The use of metal oxides in engineering and environmental research has become more popular. This study focuses on the role of TiO2 and ZnO/Ag powders on anaerobic digestion. Food waste studies on biochemical methane potential were performed with and without TiO2 and ZnO/Ag powders to examine their impact on AD. All powders are grown through the hydrothermal procedure, which has proved to be environmentally friendly and low in cost, presenting the capability to simply control the materials’ characteristics at mild temperatures. The addition of ZnO/Ag and TiO2 improved the biogas cumulative yield by 12 and 44%, respectively, compared to the control reactor. In addition, volatile solids (VS) removal efficiency increased by 5.7% in the food wastes (FW) and TiO2 reactor, while total chemical oxygen demand (TCOD) removal efficiency increased by 22% after the addition of ZnO/Ag.
The increase of source-separation of bio-waste, largely represented by food waste, and their subsequent biological treatment, is essential in waste management strategy. Aerobic and biological composting of bio-waste is a process that requires experience and technical skills, thus backyard composting can be a challenging task for the average household, with failed attempts often leading to its abandonment. Here we present the development of an integrated system including a low-cost sensor, a smart phone application, and a cloud-based service that can assist in backyard composting. The system builds on the composting-as-a-service concept. Installed in a waterproof capsule, the sensor monitors temperature at the core of the compost pile and transmits the readings to a smartphone application using Bluetooth Low Energy (BLE) technology. Based on compost temperature readings and a data feed of environmental parameters, a cloud-based service provides insight on the status of the composting process and advice for manual intervention. By supplying timely information for compost pile management, the system can increase the potential for producing a high-quality compost soil amendment and therefore the probability that backyard composting is adopted by the user. In the context of the backyard composting activity of the UIA A2UFood Project, the system is tested in a community of 100 households in Heraklion, Crete, and preliminary results are presented.
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