Economic Feasibility Of Sludge Treatment By Nitro-Hydrolysis With Product Recovery And Recycle

Activated sludge treatment facilities generate a waste stream consisting of 0.25-4% sludge, which must be disposed of as a solid waste. Conventional methods such as landfills, land farming, wet air oxidation, and incineration. The main disadvantages of such disposal methods have been the high cost of operation and aesthetic objections.

The purpose of the research was to investigate the economic and technical feasibility of utilizing a nitro-hydrolysis process as a means of sludge disposal. The nitro-hydrolysis process is based on the nitric acid hydrolysis of sludge. A generalized reaction can be written as

Sludge + HNO3 [arrow] Biodegradable organic + N₂

The hydrolysis gives a variety of carboxylic acids, mainly acetic and formic acid. The product stream contains no solid wastes. The products could either be recovered and sold commercially or recycled back to the treatment plant.

The Knoxville Utilities Board generates 65 tons of sludge, dry basis, per day. The sludge is disposed via land farms 70 miles away, difficulties in getting new land farms sites and the high cost of transportation, led KUB to consider to look for an alternate means of disposal. In this thesis, the feasibility to use nitro-hydrolysis process as an alternative disposal means, was investigated. A nitro hydrolysis process plant was designed, using a 20% solids concentration KUB sludge. The economic feasibility for both product recovery and product recycle was studied and compared to land farming and incineration

A sensitivity analysis for the process with product recovery was accomplished. The process economics depend significantly on the yield, energy, price of raw materials, capital, and inlet sludge concentration.

Due to it’s high viscosity, large solid lump compositions and fouling properties, running the process effectively could be challenging at high inlet solid concentration, if not unfeasible. The economics and design of the process was done on the assumption that the process could be run, without any major difficulties.