Fenfen Zhu

Comparison of biodiesel production from sewage sludge obtained from the A2/O and MBR processes by in situ transesterification

The potential of two types of sludge obtained from the anaerobic-anoxic-oxic (A(2)/O) and membrane bioreactor (MBR) processes as lipid feedstock for biodiesel production via in situ transesterification was investigated. Experiments were conducted to determine the optimum conditions for biodiesel yield using three-factor and four-level orthogonal and single-factor tests. Several factors, namely, methanol-to-sludge mass ratio, acid concentration, and temperature, were examined. The optimum yield of biodiesel (16.6% with a fatty acid methyl ester purity of 96.7%) from A(2)/O sludge was obtained at a methanol-to-sludge mass ratio of 10:1, a temperature of 60°C, and a H2SO4 concentration of 5% (v/v). Meanwhile, the optimum yield of biodiesel (4.2% with a fatty acid methyl ester purity of 92.7%) from MBR sludge was obtained at a methanol-to-sludge mass ratio of 8:1, a temperature of 50°C, and a H2SO4 concentration of 5% (v/v). In this research, A(2)/O technology with a primary sedimentation tank is more favorable for obtaining energy from wastewater than MBR technology.

Challenge of biodiesel production from sewage sludge catalyzed by KOH, KOH/activated carbon, and KOH/CaO

The considerable compounds content, abundance, and low costs involved has led to the proposal to use sewage sludge as raw material for biodiesel production. The transesterification reaction is catalyzed using an acid catalyst instead of base catalysts because of the high free fatty acid concentration. However, the use of a base catalyst, particularly a solid base catalyst, has certain advantages, including faster reaction speed and easier separation. In this study, we utilize in situ transesterification by base catalyst (KOH, KOH/activated carbon (AC) and KOH/CaO) with sewage sludge as raw material. Many conditions have been tested to increase biodiesel yield through single-factor tests, including mass fraction and catalyst dosage. Preliminary experiments have optimized reaction time and temperature. However, the three catalysts did not work better than H2SO4, which had a maximum yield of 4.6% (dry sewage sludge base) considering the purity by KOH, KOH/CaO, and KOH/AC. The features of the catalyst were analyzed using XRD, BETand SEM. As to BETof KOH/AC and the good spiculate formation of KOH crystal appears to be essential to its function. As for KOH/CaO, the formation of K2O and absorption points is likely essential.

Heavy metal behavior in “Washing-Calcination-Changing with Bottom Ash” system for recycling of four types of fly ashes

The Washing-Calcination-Changing with Bottom Ash (WCCB) system, effective at reducing chloride, was proposed to treat fly ash (FA) from a municipal solid waste incinerator (MSWI) before recycling FA in cement kiln as raw material. This study analyzed the behavior of heavy metals in four types of FA during WCCB treatment via Tessier and X-ray absorption fine structure (XANES) method. One FA was from the bag filter of a typical MSWI in Beijing, China (CFA), and the other three were from Japan (RFA, CaFA, and NaFA). All the metals were reduced especially Pb, Cd, and Hg (38.4-82.4%, 21.8-34.7%, and 100%, respectively). Besides Cr almost all heavy metals were stabilized according to Tessier analysis. Cr should be given more attention in WCCB as the formation of exchangeable Cr in the final residue. XANES result indicated that PbCl2 could be the main species of Pb in FA, while CaFA contains some PbO. The treated FAs contain PbCO3 and PbO besides PbCl2. The Tessier results of Ni, Pb, Cd, Cr, and Cu showed that NaFA was better at heavy metal stabilization than the other FA, so NaHCO3 is a more suitable neutralizer in WCCB.