Iwa international Specialist Conference

34.

SLUDGE COMPOSTING FOR LAND USE

Fernando Fernandes

Universidade Estadual de Londrina

Centro de Tecnologia e Urbanismo

CP 6001

CEP 86.051-990 / Londrina – PR

Brazil

The growing sewage sludge production in Brazil and the availability of agricultural soils with low organic matter contend are the most important reasons for the current use of agricultural sewage sludge recycle. Lime treatment ( 30-50% of dry weight) has been adopted in most cases by its simplicity and low cost, but the end-product is often pasty and difficult to handle.

Composting is an exothermal biological oxidation of organic matter carried out by different groups of aerobic microorganisms . The heterogeneous organic matter present in the starting material is transformed into a stabilized product through partial mineralization and humification during mesophilic (25-45 ^oC) and thermophilic ( 45-75 ^oC) stages. The ripening stage then results in a fairly homogeneous and stable end-product after a few months.
This paper presents the results of a serie of experiments of sewage sludge composting using the Windrow system ( 6 mixtures) , Aerated Static Pile system ( 3 mixtures) and In-vessel composting (3 mixtures) of sewage sludge ( 30-35% D.M.) , sawdust ( 30-70 % D.M.) and ground leaves ( 30-70 % D.M.).
For the Windrow and Aerated Static Pile systems it was used an amount of 5 m³ for each mixture.
In the Windrow system , turned each 4 days, the thermophilic stage was over after 60-70 days . For the Aerated Static Pile the thermophilic stage lasted 16-20 days.
Single high-rate composting runs were carried out in a 200-litre insulated and unheated cylindrical stainless-steel reactor. Air was forced through the system by means of an air compressor. The temperature remained in thermophilic stage for 5-8 days.
In all cases over 90% of helminth eggs were destroyed. Fecal coliform were 99% supressed and levels of heavy metals were lower than EPA part 503 limits for agricultural recycle.
Composting is a very interesting alternative for many compact activeted sludge Wastewater Treatment Plants that produces a very instable sewage sludge.

35.

The effect of food waste as a co-substrate on the variations of soluble microbial products (SMP) and extracellular polymeric substances (EPS) during anaerobic degradation of biosolids
Hyun-Woo Kim, Sun-Kee Han and Jae-Lim Lim, Hang-Sik Shin (proposed speaker)

 

Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, 373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701, Korea.

E-mail:

Hyun-Woo Kim: [e-mail] , [phone]     FAX : [phone]

Hang-Sik Shin <[e-mail]>, Tel: [phone], Fax: [phone]
The co-digestion of organic fraction of municipal solid waste (OFMSW) with sewage sludge has become popular in the past few decades. The addition of a co-substrate leads to enhanced biogas production and volatile solids (VS) reduction due to synergism. There are many candidates of synergism, such as deficient nutrient supply, toxic material dilution, biodegradability improvement, microorganism stimulation, etc. Using biological activity tests, the mixing ratio of 25% OFMSW and 75% sewage sludge was measured to be optimum for biogas production.

Among various OFMSW produced in Korea, food waste is the main source of decay, odor, and leachate in collection and transportation due to the high VS (80~90%) and moisture content (75~85%). Thus, food waste consolidated in landfills with other wastes has resulted in serious environmental problems including odor emanation, vermin attraction, toxic gas emission, groundwater contamination, etc. However, if it is used as a co-substrate in anaerobic digestion of sewage sludge, food waste could improve nutrient balance in the reaction. Moreover, sewage sludge could give a dilution effect to inhibitory materials of food waste such as volatile fatty acids, ammonia, sodium ions, etc.

Nevertheless, it is hard to explain the fundamental mechanism about the synergetic effect in co-digestion, because most studies were conducted using real complex substrates. Therefore, approaches on biomass may give more critical information about synergism than those on substrates. Soluble microbial products (SMP) and extracellular polymeric substances (EPS) are organic materials produced from microorganisms. Since a significant portion of chemical oxygen demand is shunted to EPS and SMP formation, SMP and EPS concentrations of a co-digestion process could give indirect clues for the synergetic effect.

The aim of this research was to find the effect of food waste as a co-substrate on the anaerobic degradation of sewage sludge in thermophilic and mesophilic reactors by monitoring methane production rate (MPR), SMP, EPS and other soluble COD substances. In addition, this study was attempted to verify the synergetic effect of co-substrate on the digestion using biochemical methane potential (BMP) tests.

As the proportion of food waste increased, cumulative methane production in both reactors increased, but a thermophilic reactor showed higher methane production. Also, accelerated liquefaction was observed in both reactors but a thermophilic reactor resulted in better data on the variations of DOC and VFA. The mathematically estimated optimal mixing ratios of food waste were 54.1% and 46.4%, in thermophilic and mesophilic conditions, respectively. It was confirmed that the co-digestion of food waste and sewage sludge had a distinct synergy effect on methane production rate.

The most significant advantage of synergism was nutrient balance. A confirming experiment was performed to find clues for the synergetic effect of co-substrate by monitoring the variations of SMP in the supernatant of the reactors and EPS extracted from the biomass. In this experiment, 500ml serum bottles were used and all the experimental procedures were the same. The co-digestion of food waste and sewage sludge had a distinct synergetic effect on methane production rate in the proper mixing ratio. Additional carbon sources supplied by food waste provided a more preferable environment for the growth and activity of anaerobes. In addition, an increased C/N ratio could stimulate the production of extracellular polysaccharides and proteins, resulting in improved bacterial attachment to solid surfaces.

36.

Anaerobic bioprocessing of sewage sludge, focusing on degradation of linear alkylbenzene sulfonates (LAS)
Angelidaki I., Toräng L. and Schmidt J.E.

Environment & Resources DTU, Technical University of Denmark, DK-2800 Lyngby, Denmark;

e-mail: [e-mail]; TL: [phone]; FAX: [phone]

Abstract

Anaerobic degradation of linear alkylbenzene sulfonates (LAS) was tested in continuous stirred tank reactors (CSTR) and upflow anaerobic sludge bed reactors (UASB). LAS-12 was used a model compound in the experiments. The experiments clearly showed that transformation of LAS occurred under anaerobic conditions. Degradation of LAS up to 80% was observed in the UASB reactors and up to 50% in CSTR reactors. The results from the present study are very promising as they indicate that a great potential for biological degradation of LAS is possible even at anaerobic conditions.

Introduction

Great interest has been devoted in the recent years for recycling of the waste created by modern society. A common way of recycling the organic fraction is amendment on farmland. Application of wastes on farmland is environmentally and socio-economically a very desirable solution, as wastes instead of being a burden to the societies, can be utilized as a resource for nutrients recycling and soil improvement of agricultural soils. However, if this solution is to be applied in a safe way, quality of wastes have to be good they should not contain any possible hazardous components in small amounts, which can accumulate in farming soils.
Man-made chemicals of organic origin are found widespread in the biosphere as contaminants, and their adverse effects on human health and other biological life have received increasing attention in the European Union. Many organic contaminants have broad spectrum of use in the society and a part will eventually end up in for example sewage sludge from municipal wastewater treatment plants. The main groups of contaminants that are important in respect to sludge are; Emulsifying agents as nonylphenols and nonylphenol ethoxylates (NPE), polycyclic aromatic hydrocarbons (PAHs) derived from incomplete combustion processes, phthalates, which are used as additives in plastics and surfactants such as linear alkylbenzene sulfonate (LAS).
Recent findings have detected organic contaminants in municipal sewage sludge in such concentrations that they appear toxic to many organisms due to direct exposure or due to biomagnification within the food web.

Therefore modern sewage sludge treatment must take into account these compounds and modern sewage sludge treatment has to be designed for treatment of organic contaminants.

We will present results showing possibility for bioprocessing sewage sludge to ensure optimal detoxify of the sewage sludge. We will show results from screening tests where biodegradability of selective PAH, phthalates, nonylphenol ethoxylates and LAS was tested. Finally we will focus on anaerobic degradation of LAS in CSTR and UASB reactors.

37.