Leaching characteristics of calcium-based compounds in MSWI Residues: From the viewpoint of clogging risk.

Leachate collection system (LCS) clogging caused by calcium precipitation would be disadvantageous to landfill stability and operation. Meanwhile, calcium-based compounds are the main constituents in both municipal solid waste incineration bottom ash (MSWIBA) and stabilized air pollution control residues (SAPCR), which would increase the risk of LCS clogging once these calcium-rich residues were disposed in landfills. The leaching behaviors of calcium from the four compounds and municipal solid waste incineration (MSWI) residues were studied, and the influencing factors on leaching were discussed. The results showed that pH was the crucial factor in the calcium leaching process. CaCO3 and CaSiO3 began leaching when the leachate pH decreased to less than 7 and 10, respectively, while Ca3(PO4)2 leached at pH<12. CaSO4 could hardly dissolve in the experimental conditions. Moreover, the sequence of the leaching rate for the different calcium-based compounds is as follows: CaSiO3>Ca3(PO4)2>CaCO3. The calcium leaching from the MSWIBA and SAPCR separately started from pH<7 and pH<12, resulting from CaCO3 and Ca3(PO4)2 leaching respectively, which was proven by the X-ray diffraction results. Based on the leaching characteristics of the different calcium compounds and the mineral phase of calcium in the incineration residues, simulated computation of their clogging potential was conducted, providing the theoretical basis for the risk assessment pertaining to LCS clogging in landfills.

Modulatory role of glutamic acid on the electrical activities of pain-related neurons in the hippocampal CA3 region.

Glutamic acid (Glu) participates in pain modulation of the central nervous system. The CA3 region of the hippocampal formation has been suggested to be involved in nociceptive perception. However, it is unknown whether Glu could modulate the electrical activities of pain-related neurons in the hippocampal CA3 region. The present study aimed to determine the effects of Glu and its receptor antagonist MK-801 in the pain-evoked response of both pain-excited neurons (PENs) and pain-inhibited neurons (PINs) in the hippocampal CA3 region of normal rats. We used a train of electric impulses applied to the sciatic nerve as noxious stimulation. The electrical activities of either PENs or PINs in the hippocampal CA3 region were recorded by a glass microelectrode. The results revealed that intra-CA3 region microinjection of Glu (0.5 µg/1 µl) increased the evoked firing frequency and shortened the firing latency of PEN, while decreased the evoked firing frequency and prolonged the inhibitory duration of PIN in the hippocampal CA3 region of rat evoked by the noxious stimulation. Intra-CA3 region administration of MK-801 (0.25 µg/1 µl) produced the opposite response. These results suggest that Glu and its receptors in hippocampal CA3 region are involved in the modulation of nociceptive information transmission by affecting the electric activities of PENs and PINs.