A short review on the treatment of effluents from food processing industries by electrochemical oxidation (EO) was performed. Olive mill wastewater (OMW) and boron-doped diamond (BDD) are the most reported effluent and anode material, respectively. The addition of NaCl or Na₂SO₄ as supporting electrolytes is common in these studies, and their influence on the EO performance depends, among other things, on the anode material, since the electrolyte oxidation mechanism is different when active and non-active anode materials are utilized. A case-study on the application of a pilot plant, working in batch mode with recirculation, equipped with a BDD anode, to treat 4 L of OMW, slaughterhouse (SW) and winery (WW) wastewaters, with initial chemical oxygen demands (COD) of 20.5, 3.6 and 0.26 g L⁻¹, respectively, is presented and discussed. In 16 h assays, 94% COD removal was achieved for OMW, and for SW and WW the Portuguese COD legal discharge limit of 150 mg L⁻¹ was accomplished. Process efficiency decreased for lower organic load. NaCl addition increased COD removal in SW and WW, but presented an adverse effect for OMW COD removal, when compared to Na₂SO₄ addition. Nevertheless, lower specific energy consumptions were attained in chloride medium (48 Wh (g COD)⁻¹).

The main aim of this research was to compare a bio-coagulant, organic coagulant, and a conventional coagulant applied to the treatment of leachates. Coagulant options were Stage 1 FeCl3, Stage 2 Polyamine, and Stage 3 Opuntia ficus mucilage (OFM). Optimal conditions for maximum chemical oxygen demand (COD) removal were determined by experimental data and Response Surface Methodology. The application of Multiple Criteria Decision Analysis using Multi-Criteria Matrix (MCM) was explored by evaluating the Coagulation–Flocculation processes. Maximum COD removal (%) and the best MCM scores (on a scale from 0 to 100) were: Stage 1: 69.2±0.9 and 48.50, Stage 2: 37.8±1.1 and 79.0, and Stage 3: 71.1±1.7, and 81.5. Maximum COD removal using FeCl3 and OFM was not statistically different (p 0.15 < 0.05). OFM extraction process was evaluated (yield 0.70 ± 1.17%, carbohydrate content 32.6 ± 1.18%). MCM allows the evaluation of additional technical aspects, besides oxygen COD removal, as well as economic aspects, permitting a more comprehensive analysis. Significant COD removals indicate that the use of OFM as a coagulant in the treatment of stabilized leachate was effective. Opuntia ficus cladodes, a residue, were used to treat another residue (leachates).

The presence of refractory compounds in stabilized leachates makes treatment complex. In leachate treatment systems, the lack of data on the characterization of leachates and effluents makes it difficult to track and explain the evolution of organic matter. In this study, the fractionation of chemical oxygen demand (COD) and humic substances, including humic acids (HA) and fulvic acids (FA), in addition to the application of spectroscopic techniques (Fourier transform infrared and ultraviolet–visible spectroscopy), were used to solve this data gap. A treatment system was proposed: electro-coagulation (EC) and electro-oxidation (EO). Optimal conditions (maximum COD removal) were EC, I: 4.3 A, stirring: 120 revolutions per minute, and pH: 7; EO, added NaCl: 1.0 g L⁻¹, distance between electrodes: 0.75 cm, I: 2 A, and pH: 7. Under optimal conditions COD, HA, and FA % removals were achieved: EC: 64, 69, and 63; EO: 83, 40, and 55; respectively. In EC, the % of biodegradable COD increased from 26 to 39 and in EO it increased from 39 to 58. The biodegradability index increased from 0.094 to 0.26 with EC and reached 0.46 with EO. The generated data allowed us to establish the transformations of organic matter in the process, which was useful for understanding the processes and functioning as a tool for improving treatment systems.

Sanitary landfill leachate was treated by chemical precipitation and the potential use of mixtures of the chemical precipitation sludge (CPS) generated and natural soil to cover the solid waste at sanitary landfills was evaluated. Tests were performed with soils having 0, 5 and 10% CPS, and the...

The treatment of stabilized leachates with high refractory organic matter content, which are over 10 years old, presents a challenge. This study explored the potential of electro-coagulation (EC) and electro-oxidation (EO) treatment systems to address this issue. The objective of this study was to investigate the phytotoxicity of the proposed treatment system on seed growth and examine possible relationships between phytotoxicity results and the characterization of leachates, effluents, soil, and radicles. Phytotoxicity tests were conducted on seeds of Lactuca sativa, Cucumis sativus, and Phaseolus vulgaris, using Inductively Coupled Plasma-Optical analysis. The evolution of organic matter was monitored by fractionating the chemical oxygen demand (COD) and humic substances. The biodegradability index increased from 0.094 in raw leachate to 0.26 and 0.48 with EC and EO, respectively. Removal rates of 82%, 86%, 99%, and 81% were achieved for COD, dissolved organic carbon, color, and ammoniacal nitrogen, respectively. The biodegradable COD increased from 26% in raw leachate to 39% in the EC process and 58% in the EO process effluent. The proposed treatment system successfully broke the aromatic structures of the humic substances present in the raw leachate, thereby increasing the content of biodegradable material. Phytotoxicity tests revealed that the proposed treatment system significantly reduced the phytotoxicity of the generated effluents.

The informality in brick production and fossil fuel use are environmental problems of concern. Construction and demolition waste (CDW) is included in brick manufacturing. Solar drying is an alternative to traditional fossil fuel ovens. From eight formulation mixtures, considering load resistance and 24 h water absorption tests (WA₂₄), two manufacturing mixtures were selected (mixture 2: 40% clay, CDW ¼” 60%; mixture 4: 40% clay, CDW 1 4” 50%, 10% limestone). Three drying processes were evaluated: solar, electric muffle and a traditional oven. With the traditional combustion furnace, mixture 2 obtained the highest mechanical resistance to compression (MRC), obtaining bricks for structural use (145.1 kg cm⁻²) and WA₂₄ 19.3%. Muffle drying mixture 2 obtained MRC 62.1 kg cm⁻² and WA₂₄ 18.4%. Solar drying mixture 2 obtained MRC 48.3 kg cm⁻². Although the use of the muffle and solar option resulted in bricks for non-structural use, solar drying has the environmental benefit of completely eliminating the use of fossil fuels. The proposal to include at least 50% CDW in bricks is an interesting option for upgrading these residues. In Mexico, a 10% drying implementation would lead to a reduction of 0.27 million tons of CO₂ each year.