Analyzing the design criteria of primary settlers for small sewage treatment systems: a national survey in Taiwan.

An onsite wastewater treatment facility normally has a treatment capacity of 5-200 population equivalents. The small system is receiving increasing attention in Asia countries to make up for the shortage of public sewer system. While many countries rely on large centralized system, small systems in Taiwan have significantly contributed to the treatment of municipal wastewater (21.6%) to make up for the low sewer connection (17.0%). To resolve disputes on the design criteria of primary settlers in small systems recommended by the government, a nationwide survey of 350 permit applications were conducted. This result of the survey revealed that 53% adopted self-proven criteria to reduce the size of the primary settlers using a design flow rate (Q) of 10 m(3)/d or less. The official design criteria were thus analyzed by using two new approaches of design criteria, scale-down factor and sludge blanket height ratio, as proposed in this study. The analysis indicated that sizing of primary settlers must consider the diurnal flow fluctuation and storage of settled sludge in primary settlers for a sufficient period of time, preferably up to 6 months. The official design criteria may be too conservative for Q<5m(3)/d, but inadequate for Q>20 m(3)/d. Based on the result of this study, new measures are suggested to strengthen the onsite program.

Hospital waste generation during an outbreak of severe acute respiratory syndrome in Taiwan.

During the SARS outbreak in Taiwan, the number of ambulatory patients and inpatients treated at one medical center decreased by 40%-70% because of the increasing number of SARS patients. At the peak of the epidemic, the amount of hospital infectious waste had increased from a norm of 0.85 kg per patient-day to 2.7 kg per patient-day. However, the hospital was able to return the generation of waste to normal levels within 10 days.

Analyzing the uncorrected error of dilution water demand for the dilution biochemical oxygen demand method.

Dilution water demand (DWD) can cause a positive error when the dilution biochemical oxygen demand (BOD) method is used. Dilution water demand may be attributed to oxidation of organic impurities in the dilution water and nitrification of ammonia added as a nutrient. To minimize the error associated with these sources, the standard BOD method requires that DWD be less than 0.2 mg/L in 5 days and does not allow correction for DWD when calculating test results. This study derives a set of theoretical equations to analyze the uncorrected errors with and without seeding. The authors concluded that DWD can be completely corrected if seeded dilution water is used for the sample dilution. When seeding individual bottles, the uncorrected error approaches 8.3 to approximately 8.8% at a 5-day depletion of 2 mg/L for a typical secondary effluent. Tests without seeding show an almost 1% higher uncorrected error than seeded tests. The analysis also suggests that these errors can be effectively reduced to less than 3% when the 5-day depletion approaches 6 mg/L. even for 5-day biochemical oxygen demand concentrations exceeding I x 10(4) mg/L. Further analysis indicates that, if not inhibited, the ammonium added to dilution water as a nutrient may contribute additional error due to nitrification.