Lignite aided dewatering of digested sewage sludge.

Mechanical dewatering is commonly used to increase the solids content of municipal sludge prior to its disposal. However, if the rate of filtration is slow, mechanical dewatering can be expensive. In this study, the use of lignite to improve the sludge dewatering is investigated. The effectiveness of lignite conditioning of polyelectrolyte-flocculated sludge is examined using mechanical compression tests. Results show that lignite conditioning in conjunction with polyelectrolyte flocculation gives much better dewatering than the polyelectrolyte flocculation alone. Using Darcy's filtration theory, the specific cake resistance and permeability of the compressed cakes are obtained. Both of these parameters are significantly improved after lignite conditioning. Mercury porosimetry tests on compressed cakes show that the porosity of the lignite-conditioned sludge cake is much higher than that of the polyelectrolyte-flocculated sludge and it increases with increasing doses of lignite. The mercury porosimetry results show that the lignite pore volume of pores greater than 0.5 microm are reduced with increasing sludge ratio indicating that sludge is trapped within these pores, whereas smaller pores are unaffected. The yield stress curves for sludge, lignite and sludge-lignite mixtures show that the sludge filter cake is very compressible, but the lignite-conditioned cake has a range of compressibility which although more than lignite indicate that the cake is relatively incompressible at low pressures. Thus, lignite conditioning acts to maintain the permeability of the filter cake during compression dewatering by resisting cake compression. This leads to a trade-off between the rate of dewatering and the solids content of the compressed cake. With lignite conditioning, the dewatering rate can be increased by a factor of five for the same degree of water removal.

Improving the autopsy rate at a university hospital.

PURPOSE: Although the autopsy is widely recognized as an invaluable tool for medical education, as well as the gold standard by which the accuracy of diagnoses are measured, there has been a steady decline in the autopsy rate over the last 20 years. At Westchester County Medical Center, a university hospital of New York Medical College, we observed an alarming drop in our autopsy rate. We realized that the methods used to obtain consent from the family of the deceased were haphazard and often left to the junior houseofficer available. We hypothesized that we could increase the autopsy rate by explicitly involving senior housestaff in the task of obtaining autopsy consent after giving them formal instruction in the technique of asking for consent and by having them record information regarding their encounters with families. PATIENTS AND METHODS: Data concerning the frequency of autopsies at Westchester County Medical Center were collected for a 3-month period in 1990. A corresponding period in 1991 was designated the study period during which our intervention was initiated. All medical examiner's cases were excluded for both periods since autopsy consent for these patients is not at the discretion of the family. At the start of the study period and each month thereafter, formal instruction regarding obtaining permission for autopsy was given to all senior residents assigned to direct patient care duty. The senior resident was required to complete a data form regarding autopsy request on each patient who died. RESULTS: Nine autopsies among 89 deaths (10%) were obtained during the study period in 1990, compared with 31 autopsies among 116 deaths (27%) in 1991 (p less than 0.01). In 1991, autopsies were more likely to be obtained when death was unexpected (p less than 0.05). CONCLUSION: The institution of a formal program to educate and involve the senior resident staff in obtaining autopsy consent can significantly improve the autopsy rate at a university hospital.