Quantification of hydrogen sulfide (H2S) emission strength in refuse collection point

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Quantification of hydrogen sulfide (H2S) emission strength in refuse collection point

 

Author: Wong, Tin-kam
Title: Quantification of hydrogen sulfide (H2S) emission strength in refuse collection point
Year: 1999
Subject: Hydrogen sulphide -- Environmental aspects -- China -- Hong Kong
Refuse and refuse disposal -- Environmental aspects -- China -- Hong Kong
Refuse collection -- China -- Hong Kong
Air -- Pollution -- China -- Hong Kong
Air -- Purification -- China -- Hong Kong
Odor control
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Dept. of Building Services Engineering
Pages: xvi, 76, [7] leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1485250
URI: http://theses.lib.polyu.edu.hk/handle/200/1562
Abstract: Water Scrubbers have been widely applied in the refuse collection points in Hong Kong to mitigate the odor nuisance to the resident living nearby the station by scrubbing the exhaust air with sodium hypochlorite and sodium hydroxide solution prior discharging to outside in order to reduce the hydrogen sulfide content in the exhaust air. There is a general practice in the industry by stipulating in the performance specification that the odor removal efficiency of the water scrubber is minimum 98% under the conditions of hydrogen sulfide concentration level of 25ppm at the scrubber inlet. The refuse collection point is normally provided with a ventilation rate of 30 to 40 air change per hour. These design and performance parameters are commonly required in the construction of the refuse collection points for the Provisional Urban Council, Provisional Regional Council, Housing Authority, Housing Society and private sectors developments. A refuse collection point at Shaukeiwan had been selected to study whether the hydrogen sulfide concentration inside the refuse collection point is within the occupational exposure limit set down by the Labour Department of the HKSAR and the specified odor removal efficiency of the water scrubber is adequate to mitigate the hydrogen sulfide concentration in the exhaust air. The Shaukeiwan refuse collection point had been designed to provide with a ventilation rate of 25 air change per hour, and the odor removal efficiency of the water scrubber is specified to be minimum 98%. Both the ventilation system and the water scrubber had been tested and commissioned. The performance results are satisfactory which can be complied with the specified requirements. Site measurements by using gas detector tubes to measure the concentration of hydrogen sulfide was conducted in 5 weekdays from 12th April,1999 to 16th April,1999 at various locations including the refuse collection chamber, water scrubber inlet and water scrubber outlet. Totally 44 readings of hydrogen sulfide concentration had been recorded. The results show that the hydrogen sulfide concentration inside the refuse collection chamber was ranging from 0.10ppm to 0.25ppm in the morning hours between 7:00a.m. to 8:50a.m., and was less than 0.05ppm for the rest of the day from 9:10a.m. to 11:30p.m. The maximum amount of refuse collected was on l2th April,1999 morning that 22 refuse bins were filled up with refuse. The hydrogen sulfide concentration inside the refuse collection chamber was correspondingly increased with the increase in amount of refuse being collected. The hydrogen sulfide concentration at the water scrubber outlet was less than 0.05ppm. The results demonstrate that the maximum hydrogen sulfide concentration in the refuse collection chamber was 0.25ppm which was at 2.5% of the local occupational exposure limit (OEL) of 10ppm. It is estimated that when the ventilation fan had been operated for 10 minutes, hydrogen sulfide concentration dropped to 0.006042ppm, and hydrogen sulfide concentration further dropped to 0.002260ppm for another 10 minutes of fan operation. The hydrogen sulfide concentration at the water scrubber outlet was estimated to be 0.005ppm which was at 1.0% of the specified 0.5ppm value. The results show that there are significant tolerance to reduce the ventilation air change rate in the refuse collection point. It is recommanded that the ventilation rate can be reduced to 15 air change per hour without exceeding the occupational exposure limit of the hydrogen sulfide concentration level inside the refuse collection point. The odor removal efficiency of the water scrubber can be reduced to 50% without exceeding the specified hydrogen sulfide concentration level at the water scrubber outlet. But all brands of water scrubber available in market can provide 98% odor removal efficiency and there will be no significant saving in the equipment cost. However there will be saving in the dosing cost since only half amount of the chemicals are required to react with the gaseous pollutant for reducing the odor removal efficiency of the water scrubber by one-half. It is advisable to control other gaseous pollutants such as polyethylene, carbon tetrachloride, chloroform, ketones, esters, and etc which do not react with sodium hypochlorite and sodium hydroxide in order to ensure these malodorous pollutants will not cause nuisance to the resident living nearby the RCPs. There is a survey on the recent Tender price of the water scrubbers which are to be used in refuse collection points construction and an average Tender price of HK$93,870 per m3/s flow rate capacity of water scrubber is required. The average water scrubber capacity is 7.015m3/s and a reduction of 40% in air flow rate can contribute an average saving of HK$263,400 in the construction cost of one refuse collection point.

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