A new spent coffee grounds based biochar - Persulfate catalytic system for enhancement of urea removal in reclaimed water for ultrapure water production

Powdered activated carbon (PAC)-assisted peroxymonosulfate activation for efficient urea elimination in ultrapure water production from reclaimed water

Urea is a problematic pollutant in reclaimed water for ultrapure water (UPW) production. The sulfate radical-based advanced oxidation process (SR-AOP) has been recognized as an effective method for urea degradation. However, conventional metal-based catalysts for peroxymonosulfate (PMS) activation are unsuitable for UPW production due to issues related to metal ion leaching. In this study, the use of powdered activated carbon (PAC) was investigated for the removal of urea from reclaimed water. The PAC exhibited a high degree of defects (ID/IG = 1.709) and various surface oxygen functional groups (C-OH, C=O, and C-O), which greatly enhanced its catalytic capability. The PAC significantly facilitated PMS activation in the PMS + PAC system, leading to the complete urea decomposition. The PMS + PAC system demonstrated excellent urea removal efficiency within a wide pH range, except for pH < 3. Among the various anions present, the CO32- and PO43- inhibited urea degradation, while the coexistence of Cl- promoted urea removal. Furthermore, the feasibility test was evaluated using actual reclaimed water. The quenching test revealed that SO4-·, ·OH, and O2-· played crucial roles in the degradation of urea in the PAC-assisted SR-AOP. The oxygen functional groups (C-OH and O-C=O) and defect sites of PAC clearly contributed to PMS activation.

Degradation and phosphorus immobilization treatment of organophosphate esters hazardous waste by Fe-Mn bimetallic oxide

Organophosphate esters (OPEs) waste is difficult to dispose effectively because of its stability and the potential risk of P element. In this study, taking one typical organic extractant of tributyl phosphate (TBP) as an example, we proposed a strategy to treat OPEs inspired by chemical looping combustion (CLC) technology-oxygen carrier immobilization process (OCIP), aiming at efficient TBP degradation and simultaneous P immobilization. Adopting Fe-Mn bimetallic oxide (FMBO) as oxygen carrier, an almost 100% P immobilization efficiency was achieved under recommended conditions which were obtained by response surface methodology. Meanwhile, gaseous products released from TBP degradation, e.g., non-methane hydrocarbon, was lower than the maximum allowable emission concentration limit. Further characterizations implied that P-species released from reaction process were mainly immobilized as stable inorganic forms of metaphosphate, phosphate and pyrophosphate. On the basis of identifying degradation intermediates, we proposed a possible degradation pathways. FMBO as an oxygen carrier provided sufficient oxygen molecules for flameless combustion of OCIP process. Electron paramagnetic resonance measurement confirmed the existence of oxygen vacancies on FMBO surface, which contributed to the formation of •O₂^-. Oxidation by oxygen molecules and •O₂^- attack resulted in the degradation and mineralization of TBP, with simultaneously achieving P stabilization.

The Potential of Spent Coffee Grounds @ MOFs Composite Catalyst in Efficient Activation of PMS to Remove the Tetracycline Hydrochloride from an Aqueous Solution

The efficient removal of Tetracycline Hydrochloride (TC) from wastewater, which is a difficult process, has attracted increasing attention. Aiming to synchronously achieve the goal of natural waste utilization and PMS activation, we have combined the MOFs material with waste coffee grounds (CG). The catalytic activity of the CG@ZIF-67 composite in the TC removal process was thoroughly evaluated, demonstrating that the TC removal rate could reach 96.3% within 30 min at CG@ZIF-67 composite dosage of 100 mg/L, PMS concertation of 1.0 mM, unadjusted pH 6.2, and contact temperate of 293.15 K. The ¹O₂ and ·SO₄^- in the CG@ZIF-67/PMS/TC system would play the crucial role in the TC degradation process, with ¹O₂ acting as the primary ROS. The oxygen-containing functional groups and graphite N on the surface of CG@ZIF-67 composite would play a major role in efficiently activating PMS and correspondingly degrading TC. In addition, the CG@ZIF-67/PMS/TC system could withstand a wide pH range (3-11). The application of CG in preparing MOF-based composites will provide a new method of removing emerging pollutants from an aqueous solution.

Energy recovery and waste treatment using the co-pyrolysis of biomass waste and polymer

The pyrolysis of spent coffee grounds (SCG) and polymers was examined as a waste treatment option for energy recovery and carbon sequestration. Rice straw-derived biochar was used as control biochar to evaluate the sorption capacity and energy production capability of SCG-derived biochar. SCG are characterised by high levels of volatile matter, rendering them suitable as an energy source. SCG were converted to biochar, bio-oil, and syngas via pyrolysis, with yields of 22%, 33%, and 45%, respectively. The high heating value (HHV) of the biochar and bio-oil was 20.6 and 22.9 MJ kg^-1, respectively, indicating that they could be used as supplementary fuels. Co-pyrolysis with polymers (20 v v%^-1) increased the HHV of biochar. Accordingly, the maximum production of CH₄ and H₂ increased from 0.3 and 0.04 mmol g^-1 to 3.4-6.3 and 0.8-1.3 mmol g^-1, respectively. Polystyrene most strongly enhanced the yields of CH₄ and H₂, followed by polypropylene and polyethylene; this order was likely to be in accordance with the number of carbon and hydrogen atoms present in the monomers. Similar to rice straw-derived biochar, the biochar produced from SCG demonstrated a high sorption capacity for 2,4-dinitrotoluene and chromate due to its high carbon content and anion exchange capacity, respectively. Laboratory pot tests revealed that the coffee grounds-derived biochar was able to increase the growth of young radish. Our results suggest that the pyrolysis of SCG and polymer may be a promising option for waste treatment, energy production, and carbon sequestration.

Towards the sustainable and circular bioeconomy: Insights on spent coffee grounds valorization

Discovered in Ethiopia, coffee became a popular beverage in Asia, Europe, Latin America, Australia, Africa and the North America as a drink after water and the largest goods after petroleum. However, the coffee industry generates a huge biomass as its byproducts of which the spent coffee grounds (SCG) is concerning, especially in the production chain away from the farm. Therefore, the valorization and revalorization of the SCG has a huge impact on the socioeconomic and environmental sustainability of the industry, up to the realization of the circular bioeconomy. With the advancing biorefinery concept, even an almost complete recovery of the SCG is reported at an experimental level. Such kind of studies increased with time following the action of the Sustainable Development Goals by the United Nations Development Program promulgated in 2015. The current review highlights on the background, socioeconomic, environmental contexts of coffee production and the SCG valorization and revalorization studies. Refereeing to 154 screened articles published in over 30 years' time, the SCG revalorization efforts and its integrated biorefinery as a green management approach are uniquely addressed. Plenty of studies have reported the production of bio-products from the SCG, such as the derivation of adsorbents, biochar, bioethanol, biogas, biodiesel, bio-oil, compost, construction material aggregates, cosmetics, electricity and food ingredients. In conclusion, the recovery potential of the SCG is promising and can substantially contribute to a sustainable and green bioeconomy. Nevertheless, the recovery of bioactive materials through SCG fermentation is still lacking. Most studies are conducted on a lab scale, which needs to be piloted and commissioned. Furthermore, the link between climate change and variability vis-à-vis the sustainable management of the SCG remains unaddressed.