| Biological nutrients obtained through Sewage | | | | the quantity of Ammonia, and this will in turn increase |
| treatment have long been used as fertilizer for | | | | the quantity of Nitrate as well as Nitrite in the |
| growing a variety of crops. In this article I discuss the | | | | effluent. |
| pros and cons of using such nutrients to grow plants: | | | | 3) Certain toxic elements of the sludge degrading |
| In treatment plants, organic matter in Sewage is | | | | during the treatment process may not necessarily |
| decomposed by microorganisms and the residue is | | | | reduce the level of toxicity but merely convert the |
| deposited as sludge. This sludge is rich in biological | | | | elements from one form to another. |
| nutrients. Solid particles in the sludge that's been | | | | 4) Ultimately the treated waste may be dosed with |
| stabilized and settled during the treatment process | | | | Chlorine to disinfect it. The residual Chlorine that will |
| are called bio solids. They contain organic and | | | | remain in the Sewage can affect fish adversely, |
| inorganic particles. The plant nutrients in bio solids | | | | where the Sewage after treatment is discharged into |
| makes them popular as fertilizer. However toxins and | | | | water bodies. |
| heavy metals tend to get added to biosolids. So | | | | In the final analysis, however, I wouldn't recommend |
| biosolids need to be tested frequently for the | | | | re-using sludge as manure, for the following reasons: |
| presence of these contaminants as well as refractory | | | | (i) Worldwide, authorities dealing with environment |
| organics, before biosolids can be used as fertilser. | | | | protection and / or pollution control are concerned |
| This sludge can either be incinerated or solidified for | | | | about the high incidence of STP owners who pass |
| the purpose of disposal. Or it can be treated using an | | | | off bad quality sludge as fit for use as manure. Often |
| anaerobic process. | | | | such sludge is polluted by unacceptable levels of |
| Following are some derivatives obtained from | | | | heavy metals, and, over time, could damage the soil |
| treatment of Sewage; such treatment may involve | | | | and ground water. |
| both physical and chemical processes. | | | | (ii) STP sludge does not have ready buyers either for |
| 1) When the activated sludge process is used for | | | | use as manure or for sale after mixing it with |
| secondary treatment, it might increase the content | | | | conventional manure. |
| of Ammonia. This can happen because the organic | | | | Go ahead and use sludge as manure only if you are |
| material gets converted into Ammonia Nitrogen which | | | | able to convince the local authority about the quality |
| eventually gets reduced to Nitrogen. | | | | of your sludge and reliability of your treatment |
| 2) A nitrification process can be used to decrease | | | | process that produces it. |