Kinetic Modeling and Mechanisms of Manganese Removal from Alkaline Mine Water Using a Pilot Scale Column Reactor

Manganese (Mn) is a major element in various aqueous and soil environments that is sometimes highly concentrated in mine water and other mineral processing wastewater. In this study, we investigated Mn removal from alkaline mine water (pH > 9) with an Mn-coated silica sand packed into a pilot-scale column reactor and examined the specific reaction mechanism using X-ray absorption near-edge structure (XANES) analysis and geochemical kinetic modeling. The kinetic effect of dissolved Mn(II) removal by birnessite (δ-Mn(IV)O2) at pH 6 and 8 was evaluated at different Mn(II)/Mn(IV) molar ratios of 0.1–10. Our results confirmed the positive effect of the presence of δ-MnO2 on the short-term removal (60 min) of dissolved Mn. XANES analysis results revealed that δ-MnO2 was more abundant than Mn(III)OOH in the reactor, which may have accumulated during a long-term reaction (4 months) after the reactor was turned on. A gradual decrease in dissolved Mn(II) concentration with depth was observed in the reactor, and comparison with the kinetic modeling result confirmed that δ-MnO2 interaction was the dominant Mn removal mechanism. Our results show that δ-MnO2 contents could play a significant role in controlling Mn removability from mine water in the reactor.

Simultaneously Recovery of Phosphorus and Potassium Using Bubble Column Reactor as Struvite-K and Implementation on Crop Growth

Struvite-K, similar to NH4-struvite with a composition of Mg:K:P (1:1:1). It is called struvite-K because the K replaces the NH4 in struvite. The composition usually used as fertilizer and can be recycling from wastewater including livestock wastewaters. In addition, Struvite-K which tends to form scale on surfaces of equipment which problem in many industries. The present study was used bubble column reactor which simple and efficient. In addition, the process can be implementation in wastewater industry which low-tech processes. Then, the struvite-K precipitate was implementation on crop growth which compared with coffee husk compost. The results show the removal of P via struvite-K showed 98.5% with the precipitation Mg:P of 0.7 and K:P of 1 with yields of 11.28 gram. Increases of magnesium dosage which decreases of P removal rate and affected of crystal size structure. Compost and struvite-K have similar positive impact on crop growth of (radish and komatsuna) were compared than control. In the other hand, the struvite-K is more effective than compost. This might be indicated that struvite-K is more slow-release nutrient than compost and higher macro nutrient supplied on soil which crop needed.

Optimization of In-situ Transesterification Process for Biodiesel Production from High Free Fatty Acid Feedstock by Semi-continuous Column Reactor

An in-situ transesterification (in-situ TE) process can reduce the multiple steps of biodiesel production by merging vegetable oil extraction and biodiesel synthesis into a single step. However, high free fatty acid, generally found in waste feedstock, dramatically reduce both yield and quality of biodiesel. In this work the new concept of a semi-continuous column reactor was introduced to mitigate the negative effect of high free fatty acid found in spent coffee grounds (SCGs). The potassium methoxide solution, as reactive solvent, was pumped through the series of column reactors. At the beginning of process free fatty acid in SCGs was promptly extracted in form of soap as a pretreatment fraction. Then, the residual mono-, di- and triglyceride in SCGs matrix were covert to fatty acid methyl ester (FAME) biodiesel and simultaneously extracted. A liquid fraction analysis was conducted to distinguish the pretreatment fraction from biodiesel. A central composited rotatable design was applied to determine optimal process conditions of potassium methoxide concentration and solid retention time at 30°C. Under the optimal conditions, up to 88% FAME yield was observed. The residual triglyceride in defatted SCGs was less than 1.5%mass. Compared to batch reactor type, the semi-continuous column reactor used only half of the required methanol for in-situ TE by recirculating the reagent in the series of reactors. This could dramatically reduce the energy usage and environmental impact of FAME production from high free fatty acid feedstock via in-situ TE.