Land Application of 



BIOSOLIDS 



Tom Buoh 



There has been increasing interest in utilizing 

 waste products as fertilizer substitutes, in the 

 case of biosolids (treated waste products from 

 water and wastewater treatment plants), there can be 

 advantages for both the producers and the users. For 

 municipalities, land spreading can be the least expen- 

 sive method of waste disposal, and for land owners, 

 applying biosolids can be an inexpensive way to ob- 

 tain needed nutrients for crop production. 



When evaluating whether or not the use of 

 biosolids will be advantageous to you, there are vari- 

 ous factors that need to be considered. Since the land 

 application of any waste product can be controversial, 

 one needs to be aware of the social and legal as- 

 pects, as well as the scientific. I will only be discuss- 

 ing some of the technical considerations. 



The first factor to consider is whether or not the 

 product is of high quality, in the case of biosolids, 

 this pertains to the nutrient content, the presence of 

 heavy metal, and the absence of pathogens. iVlost of 

 the biosolid materials available tend to be fairly high 

 in nutrient content, but this will vary from one source 

 to another and from one treatment regime to another. 

 The heavy metal contents also vary and are somewhat 

 dependent on the type of industry located in the mu- 

 nicipality. The latest federal regulations (EPA 503 

 regs) have placed limits on heavy metals concentra- 

 tions for biosolids for land applications. Only materi- 

 als which are below these levels can be applied. 

 Along with this, waste materials have to be treated to 

 reduce pathogen levels prior to land application. 



From a nutrient standpoint, biosolids tend to be 

 high in nitrogen, phosphorus and calcium, but very 

 low in potassium. Depending on what treatment pro- 



cess is used, the pH can vary from neutral (7.0) to 

 very high (12.0). The high calcium and pH levels are 

 associated with the lime stabilization process to re- 

 duce pathogen levels. The nitrogen exists in the or- 

 ganic form, which means that it releases slowly over 

 time, depending on temperature and moisture condi- 

 tions. This has advantages and disadvantages, de- 

 pending on the situation. 



Since only high-quality (nutrient-rich, low-metal, 

 pathogen-free) biosolids should be used in a land ap- 

 plication program, it is likely that the application rate 

 will be limited by the nitrogen concentration and not 

 heavy metal concentrations. This means that the 

 amount of biosolids applied will depend on the nitro- 

 gen requirement of the crop to be planted and the ni- 

 trogen content of the biosolid material being consid- 

 ered. A corn crop would certainly have a higher re- 

 quirement than a grass sod crop, so the application 

 rates would be quite different. As mentioned earlier, 

 the slow-release characteristics of the nitrogen fit 

 quite well the recommendations for many crops, but it 

 is important to carefully estimate the nitrogen from 

 other sources. If the amount of nitrogen in the soil is 

 more than the plants can use, it creates the risk of 

 greater leaching. And this may pose an increased risk 

 of groundwater contamination. 



The actual application of biosolids to land will de- 

 pend on the physical characteristics of the material 

 being used (solid or liquid) and the equipment avail- 

 able for spreading. It is very important that the mate- 

 rial be spread evenly over the area to avoid pockets 

 of nutrient concentrations above the recommended 

 rates. 



In agricultural operations, biosolids will be only one 



20 



The Plantsman 



