Abstract
The challenges in managing sludge produced from wastewater treatment plants (WWTP’s) are beginning to increase rapidly in the Balkans and Eastern Europe as countries act to treat wastewater to levels that would comply with the Water Framework Directive of the European Union. Organic wastes, such as WWTP sludge, various organic animal wastes, as well as organic materials being generated from biogas plants, contain a variety of pathogenic microorganisms, which can spread various diseases in humans and animals.
This paper will describe an approach which uses a variety of organic wastes to arrive at specified, combined organic-mineral fertilizer, which is well suited to agricultural applications. The approach to be described in the paper takes place in four (4) stages:
Stage 1: Classic pasteurization of organic waste by the application of lime (CaO) based on the mixture of each organic material being used and according to their unique constituents.
Stage 2: Stabilization of the residual pH to a range of 7-8 through the use of a citric acid source.
Stage 3: The introduction of natural zeolite with a percent solids of 10-40%
Stage 4: Drying and pelletezation of the final, stabilized material for ease of handling and later application.
The final product achieved is an “organic fertilizer” that can be “tailored” as to its constituents and characteristics to comply with the standards and norms used for farming and agricultural purposes. The entire treatment process is linear in nature, and can be accomplished with an overall retention time of 3-4 hours. The process has been proven at scale and the fertilizer products have been analyzed to support the overall effectiveness and economics of the process as a low cost, bio-solids reuse technology.
Keywords: Sludge, Organic Waste, Microorganism Pathogens, Lime (CaO), Zeolite, Fertilizer.
Introduction
The study was performed during the period from 2009-2014, during the implementation of the Project “Treatment and Processing of Municipal Sludge from the Wastewater Treatment Plant Vranishta” in Struga, Republic of Macedonia. This study was performed in two stages, as follows:
The dewatering technology applied to the settled sludge at the sludge source facility (Vranista Wastewater Treatment Plant) for this research is a belt filter press, which produces a sludge solid in the range of 15-25% dry solids with a composition of 53% organic matter and 47% inorganic materials.
In the first phase, the goal of the research was to obtain a microbiologically acceptable sludge material which could then be used for fertilizer, which would be composed of an organic component to supplement the organics that are increasingly lacking in worn-out soils, as a result of using purely inorganic fertilizers, and a mineral component that would contain the elements necessary for plant cultures. The important factor in the research was to assure that the new product, to be applied to the land, does not change the composition of the agricultural land.
The second phase of the research was focused on the effects of the new combined organic-mineral fertilizer product, on vegetable crops, soil impacts, and economic viability of its use.
