Combined use of reactive barrier and electrokinetics for remediation of Cr contaminated soil

A reactive barrier (RB) of transformed red mud (TRM), a by-product of the refinement of bauxite in alumina production, was fitted adjacent to the anode of an electrokinetic (EK) system with the aim of enhancing removal and favouring entrapment of chromium added to a low permeability clayey soil. The innovative study focused on evaluation of the synergic interaction between the EK system and the RB, and of efficiency when compared to traditional EK remediation. The results obtained underlined the successful outcome of treatment. In presence of the TRM RB, 19.4% wt. of total Cr content was detected in the anolyte and 20.6% wt. trapped in the anodic RB after 6 days, versus 6.6% wt. in the anolyte and 8.8% wt. in the soil adjacent to the anode following the control run without RB. On increasing duration of treatment up to 12 days, 60.8% wt. of total initial Cr was found in the anolyte and 25.5% wt. trapped in the RB, versus 9.1% wt. and 5.3% wt., respectively, after a control run of the same duration. Finally, on increasing the mass of TRM in the RB, 60.6% wt. of initial Cr content was found to have accumulated in the RB, with Cr being completely absent from the anodic chamber

Energy recovery from one- and two-stage anaerobic digestion of food waste

Abstract One- and two-stage anaerobic digestion of food waste aimed at recovering methane (CH4) and hydrogen and methane (H2 + CH4), respectively, were compared in order to assess the potential benefits from the two-stage process in terms of overall energy recovery. Results suggest that a two-stage process where the first reactor is properly operated in order to achieve a significant net hydrogen production, may display a 20% comparatively higher energy recovery yield as a result, mainly, of enhanced methane production as well as of the associated hydrogen production. The highest methane production of the two-stage process was due to improved hydrolysis and fermentation of food waste, with increased amounts of volatile fatty acids being readily available to methanogenesis

Co-composting of municipal biowaste and biomass power plant ash: effect on the biological process and the final compost quality

In this work the use of selected types of biomass combustion ash as an additive in the composting process was studied and discussed. A composting experimental campaign was conducted in four pilot-scale composters where 0%, 2%, 4% and 8% (w/w) of biomass ash were added to the organic fraction of the municipal solid waste mixed with wood prunings, that served as bulking agent. Biomass ash influenced both the composting process and the final product quality positively. The volatile solids reduction and the stability of the final composts, the latter being measured by means of the oxygen consumption, were greatly enhanced, and the temperature rise at the early stage of the process was improved. The ash-amended composts were enriched in nutrients (Ca, Mg, K and P) and expected to be beneficial for the plant growth, as the germination tests showed. Some adverse effects were also observed, such as the higher pH and electrical conductivity in the ash-amended composts comparing to the unamended one. Also, moisture was greatly affected by ash addition, to an extent which required external control. As for the heavy metal content, that was expected to be the main disadvantage related to the ash use, it does not seem to constitute an environmental concern for the ash content considere

REUSE OF BIOMASS ASH AS AN ADDITIVE IN THE COMPOSTING PROCESS

This work investigated the effects of using selected types of biomass combustion ash as an additive in the composting process. An experimental campaign was conducted where source separated organic fractions of municipal waste was mixed with 0%, 2%, 4% and 8% (w/w) of biomass ash. Both the composting process and the final compost quality were positively influenced by ash addition. In the ash-amended composting admixtures a higher volatile solids degradation and enhanced biological stability were found, because ash were found to be effective as physical conditioner. Improved humification of the organic matter, better germination performances and higher total Ca, Mg, K and P contents were observed in the ash-amended composts comparing to the unamended one. In addition, nutrients fraction readily availability for plants was favored by ash addition with regards to Ca, Mg and K. Nitrogen content in the final composts was reduced by ash addition, but the Ctotal/Ntotal ratio was not negatively affected. The content of heavy metals and their solubility, that is regarded as the main environmental disadvantage when using combustion ash as additive, did not affect the final compost quality negatively. On the other hand, some controversial effects were observed, such as higher pH and electrical conductivity levels comparing to the unamended one. Moreover, higher temperature values and lower moisture levels were observed at the beginning of the composting process in the ash-amended composting admixture

Effect of inoculum to substrate ratio (ISR) on hydrogen production through dark fermentation of food waste

The objective of the present study is to evaluate the influence of the inoculum to substrate ratio (ISR) on hydrogen production through dark fermentation of food waste (FW). Batch tests were performed adopting ISR values ranging between 0.05 and 0.25 g VSINOCULUM/g VSSUBSTRATE under mesophilic conditions (39°C) and adopting a pH set-point value of 6.5. Activated sludge was used as inoculum without any pre-treatment aimed at harvesting specific hydrogenogenic biomass. The obtained results underlined that an appropriate choice of the ISR was essential in order to increase H2 yield, to decrease lag phase duration and to maximize the mass of FW treated in the reactor. The best performance in terms of H2 yield (88.8 Nl H2/kg VSFW) was observed at ISR = 0.14 g VS INOCULUM/g VS SUBSTRATE