Our experience with sewage sludge has indicated an analysis of VERY much less than 1-1-1. This means that many tons per acre or a ton or more per 1,000 sq. ft. are required to significantly contribute to the soil's fertility. Good for the municipalities. Logistically problematic for many growers. However, in the Austin area and no doubt many other places, sludge is quite popular. In a recent local newspaper article, several farmers extolled the virtues of it.
In the samples we have tested, we've seen no significant amounts of heavy metals.
Our concern, and the concern of our biological inoculants grower client, is with what we cannot analyze: the long-chain complex, often organic molecules - pesticides, chemicals, antibiotics, other drugs and everything else people don't want and flush down the sewer. A lot of these things don't evaporate and break down only very slowly, if at all.
Being as how biology (microbes) is a big part of our fertility programs for commercial growers, we are extremely cautious about recommending material with uncertain pedigrees.
