Waste Treatment by Irradiation

To make sewage sludge compatible with plant life in an environmentally friendly way and also to make it usable as a safe soil conditioner, it is desirable to convert it into living humus by aerobic composting. Irradiation of sludge cake and subsequent composting have revealed the following (see Kawakami et al., 1981)  

The optimum processing conditions are at temperatures -50 °C, pH -7-8 and an irradiation dose around 5 KGy. Irradiation of dewatered sludge can reduce irradiation costs. 

Since irradiated sludge does not compost by itself, it is necessary to introduce a seed. The composted product can act as a seed. There is no significant difference between the composting characteristics of unirradiated or irradiated sludge when seeded similarly. Repeated use of composted sludge as seeds has no detrimental effects. 

C02 and NH3 evolutions occur almost simultaneously. Their rate of evolution reaches a maximum at about ten hours after irradiation and evolution ceases after about three days under optimal conditions. 

Irradiation shortens the composting period, because it is not necessary to keep an elevated fermentation temperature to reduce the pathogens in the sludge. 

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