Adaptation of urine source separation in tropical cities: Process optimization and odor mitigation

Source-separating urine from other domestic wastewaters promotes a more sustainable municipal wastewater treatment system. This study investigated the feasibility and potential issues of applying a urine source-separation system in tropical urban settings. The results showed that source-separated urine underwent rapid urea-hydrolysis (ureolysis) at temperatures between 34–40^oC, stale/fresh urine ratios greater than 40%, and/or with slight fecal cross-contamination. Undiluted (or low-diluted) urine favored ureolysis; this can be monitored by measuring conductivity as a reliable and efficient indicator. The optimized parameters demonstrated that an effective urine source-separation system is achievable in tropical urban areas. On the other hand, the initial release of CO₂ and NH₃ led to an elevated pressure in the headspace of the collection reservoir, which then dropped to a negative value, primarily due to oxygen depletion by the microbial activity in the gradually alkalized urine. Another potential odor source during the ureolysis process was derived from the high production of volatile fatty acids (VFA), which were mainly acetic, propanoic, and butyric acids. Health concerns related to odor issues might limit the application of source separation systems in urban areas; it is therefore vital to systematically monitor and control the odor emissions from a source separation system. As such, an enhanced ureolysis process can attenuate the odor emissions.

Implications: Urine source separation is promising to improve the management of domestic wastewater in a more sustainable way. The work demonstrates the achievability of an effective urine source-separation system in tropical urban areas. The installation of urine-stabilization tanks beneath high-rise buildings lowers the risk of pipe clogging. Conductivity measurement can be utilized as a reliable process indicator for an automated system. However, urine hydrolysis raises a strong potential of odor emission (both inorganic and organic), which might limit the application of source separation systems in urban areas. An enhanced ureolysis process could shorten and attenuate the odor emissions.     

Ethanol production from potato peel waste (PPW)

Considerable concern is caused by the problem of potato peel waste (PPW) to potato industries in Europe. An integrated, environmentally-friendly solution is yet to be found and is currently undergoing investigation. Potato peel is a zero value waste produced by potato processing plants. However, bio-ethanol produced from potato wastes has a large potential market. If Federal Government regulations are adopted in light of the Kyoto agreement, the mandatory blending of bio-ethanol with traditional gasoline in amounts up to 10% will result in a demand for large quantities of bio-ethanol. PPW contain sufficient quantities of starch, cellulose, hemicellulose and fermentable sugars to warrant use as an ethanol feedstock. In the present study, a number of batches of PPW were hydrolyzed with various enzymes and/or acid, and fermented by Saccharomyces cerevisae var. bayanus to determine fermentability and ethanol production. Enzymatic hydrolysis with a combination of three enzymes, released 18.5 g L^?1 reducing sugar and produced 7.6 g L^?1 of ethanol after fermentation. The results demonstrate that PPW, a by-product of the potato industry features a high potential for ethanol production.     

Adsorption of Cu(II) ions from aqueous solutions on biochars prepared from agricultural by-products

In this study, the adsorption of Cu(II) from aqueous solutions by agricultural by-products, such as rice husks, olive pomace and orange waste, as well as compost, was evaluated. The aim was to obtain sorbent materials (biochars) through hydrothermal treatment (300?°C) and pyrolysis (300?°C and 600?°C). The effect of adsorbent dose, pH, contact time and initial Cu(II) concentration in batch-mode experiments was investigated. The optimum Cu(II) adsorption conditions was found to occur at 5-12?g/L adsorbent dose, initial pH 5-6, and reaction time 2-4?h. Furthermore, the adsorption kinetics were best described by the pseudo-second order model for all the tested materials, while the adsorption equilibrium best fitted by the linear and Freundlich isotherms. Comparing rice husks and olive pomace, the higher adsorption capacity resulted after pyrolysis at 300?°C. With respect to the orange waste and compost, the highest adsorption capacity was observed using biochars obtained after hydrothermal treatment and pyrolysis at 300?°C.     

Transport of cadmium and assessment of phytotoxicity after electrokinetic remediation

The use of ethylene diamine tetraacetic acid (EDTA) on the electrokinetic removal of cadmium-contaminated soil was evaluated. A total of four different tests were conducted using EDTA as a washing solution as well as a purging solution at the electrode compartments. The efficiency of electrokinetic extraction was significantly influenced by the pH of the soil medium. The results show that EDTA was effective in desorbing cadmium at a high pH, with Cd-EDTA(-) anion complexes migrating toward the anode. At low pH values near the anode area, cadmium existed as Cd(2+), migrating toward the cathode. Such contradicting directions of cadmium have resulted in its detrimental removal from the soil cell. However, accumulation of cadmium near the cathode was observed at the end of the tests due to the dominating low pH in the soil cell. The phytotoxicity after the electrokinetic process was investigated using Sorghum saccharatum, Lepidium sativum and Sinapis alba plants. The germination index was a major endpoint estimated by measuring seed germination and shoot elongation. The results obtained show that the phytotoxicity was increased after electrokinetic extraction. Despite, the extensive cadmium removal from two-thirds of the cell, the low pH of the soil was the principal parameter exhibiting the phytotoxicity.     

Detoxification of tannery waste liquors with an electrolysis system

This paper describes an electrochemical treatment and detoxification of tannery waste liquors (TWL). In this technique, TWL was passed through an electrolytic cell using a Ti/Pt anode and a stainless steel 304 cathode. Owing to the strong oxidizing potential of the chemicals produced (chlorine, oxygen, hydroxyl radicals and other oxidants) the organic and inorganic pollutants (ammonia, sulfides and chromium) were wet oxidized to carbon dioxide, nitrogen oxides and sulfur dioxide. In addition, chromium was precipitated as Cr(2)(SO(4))(3). Experiments were run in a batch, laboratory-scale, pilot-plant, and the results are reported herein. After 30 min and 3 h of electrolysis at 0.26 A cm(-2), 45 degrees C and pH 9, total chemical oxygen demand (COD) was reduced by 52 and 83% and biochemical oxygen demand (BOD(5)) was reduced by 35 and 66%, respectively. Additionally, total suspended solids (TSS) were reduced by 8.6 and 26%, total phenolic compounds were reduced by 95.6 and 99.4%. Ammonia, sulfides and soluble chromium were reduced by 100% in both cases, while the mean anode efficiency was 81 g h(-1) A(-1) m(-2) and 1.9 g h(-1) A(-1) m(-2). Also, the mean energy consumption was 4.8 kwh kg(-1) of COD reduced and 200 kwh kg(-1) of COD reduced for 0.5 and 3 h, respectively. These results strongly indicate that this electrolytic method of total oxidation of TWL cannot be cost effective for wide use. However, it can be used as an effective pretreatment stage for detoxification of the wastewater, owing to great efficiency especially with respect to COD and toxicity (phenolics) reduction.