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The effect of formaldehyde use in sanitation
Expanded Title:Formaldehyde is a simple CH2O molecule which ranks amongst the 25 highest volume chemicals produced in the USA, with the annual production in the USA around 1.4 million tons at the turn of the century. It highest use is for the production of resins, followed by the industrial synthesis of many organic compounds. For the period 1992 to 2009, South Africa was a net exporter of formaldehyde of an average of 100 tons per year. The amount of formaldehyde produced in South Africa could not be determined. When bought in bulk, the price of formalin (a 37% formaldehyde solution), is less than that of petrol or diesel. Formaldehyde does not raise any serious human health or environmental concerns, provided it is properly handled and stored. When released into the air, it is rapidly broken down by photolysis. When released into water, it is biodegraded within a few days. It is a well regulated chemical with extensive standards in different environments. Formaldehyde finds extensive use in chemical toilets. The holding tank is dosed with chemicals, which inhibit the biological degradation of the waste and also add a satisfying fragrance to the wastewater. Most of the commonly used holding-tank chemicals contain formaldehyde and are toxic or inhibitory to wastewater at full strength, but completely biodegrades with dilution and time. It breaks down into simpler molecules (like carbon dioxide and water) through the natural action of oxygen, sunlight, bacteria and heat. The biodegradation is considered to be faster than most other deodorant products, and therefore formaldehyde-based products are considered the most effective holding tank chemicals available. It was not possible to determine how much of these formaldehyde-based toilet chemicals are used in South Africa every year. First, the formaldehyde content of the products varies widely. Second, there are some “formaldehyde-free” chemicals which appropriate an unknown part of the market share. Third, suppliers and users of these chemicals were not forthcoming in providing such information, despite repeated attempts. The addition of chemical toilet waste to biological wastewater treatment facilities poses two potential problems. First, the waste from chemical toilets is about 20 times more concentrated than that of normal domestic wastewater. Second, the presence of formaldehyde in the waste may inhibit the biological activity in the wastewater treatment facility. If the volume of chemical toilet waste is large in relation to the capacity of the treatment plant, its discharge could upset the proper working of the plant. For shock loads of formaldehyde to aerobic systems, the half-kill dose (= 50 % reduction in biological activity) is as much as 200 mg/liter. For continuous loading, the minimum half-kill dose is reported as about 20 mg/liter, but bacteria will acclimate to eventually remove larger concentrations of formaldehyde. For anaerobic treatment, the critical formaldehyde concentration is slightly higher than for aerobic treatment. When formaldehyde is discharged to septic tanks, it could lead to bacterial die-off and clogging of the French drain. The critical concentration is reported to be about 250 mg/liter, which is much higher than the estimated values of formaldehyde in chemical toilets. Normal wastewater treatment facilities should never come close to these concentrations. An interesting case study is offered by the new King Shaka airport near Durban. The airport has a small, dedicated wastewater treatment plant for the airport, which also accepts the wastewater from 3.7 million airline passengers per annum. Even in this extreme case, the aircraft wastewater amounts to about 1.2% of the total inflow. The chemicals added to the aircraft holding tanks are diluted to 0.1%, which means that the chemical concentration entering the wastewater treatment plant, even with the assumption of no biodegradation, is only about 0.001 mg/liter. The overall conclusion is that the use of formaldehyde in chemical toilets does not pose a problem to normal wastewater treatment facilities below a conservative estimate of say 20 mg/liter, whether it is a septic tank, aerobic treatment or anaerobic treatment. Given the low concentration of formaldehyde in the chemicals used, the large dilution when added to the holding tanks, and the rapid biodegradation of formaldehyde in a wastewater environment, this is a value which is very unlikely to be reached, of which no examples could be found. Even in the unusual case of King Shaka airport, the levels of formaldehyde is at least about four orders of magnitude lower than the level suggested. After a preliminary quantification of the concentrations of formaldehyde discharged to wastewater treatment facilities, there is no reason to believe that this is an imminent problem. No further studies are warranted at this time.
Date Published:01/07/2011
Document Type:Research Report
Document Subjects:Wastewater Management - Domestic, Wastewater Management - Sewers, Sanitation - On site sanitation, Sanitation - Hygiene
Document Format:Report
Document File Type:pdf
Research Report Type:Consultant
WRC Report No:KV 274/11
ISBN No:978-1-4312-0123-5
Authors:Crous PA; Haarhoff J
Project No:K8/949
Organizations:University of Johannesburg
Document Size:912 KB
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