VILNIUS GEDIMINAS TECHNICAL UNIVERSITY

Eglė ZUOKAITĖ

INVESTIGATIONS OF COMPOSTED SEWAGE SLUDGE AND WAYS TO REDUCE GASEOUS EMISSIONS SUMMARY OF DOCTORAL DISSERTATION TECHNOLOGICAL SCIENCES, ENVIRONMENTAL ENGINEERING (04T)

Vilnius 2011

Doctoral dissertation was prepared at Vilnius Gediminas Technical University in 2007–2011. Scientific Supervisor

Assoc Prof Dr Aušra ZIGMONTIENĖ (Vilnius Gediminas Technical University, Technological Sciences, Environmental Engineering – 04T).

Consultant Assoc Prof Dr Dainius PALIULIS (Vilnius Gediminas Technical University, Technological Sciences, Environmental Engineering – 04T).

The dissertation is being defended at the Council of Scientific Field of Environmental Engineering at Vilnius Gediminas Technical University: Chairman

Prof Dr Habil Pranas BALTRĖNAS (Vilnius Gediminas Technical University, Technological Sciences, Environmental Engineering – 04T).

Members: Assoc Prof Dr Paulius KERPAUSKAS (Aleksandras Stulginskis University, Technological Sciences, Environmental Engineering – 04T), Assoc Prof Dr Mindaugas RIMEIKA (Vilnius Gediminas Technical University, Technological Sciences, Environmental Engineering – 04T), Prof Dr Habil Petras VAITIEKŪNAS (Vilnius Gediminas Technical University, Technological Sciences, Environmental Engineering – 04T), Prof Dr Habil Vytenis Albertas ZABUKAS (Klaipėda University, Technological Sciences, Environmental Engineering – 04T).

Opponents: Dr Nijolė KAZLAUSKIENĖ (Nature Research Centre, Biomedical Sciences, Ecology and Environmental Studies – 03B), Prof Dr Saulius VASAREVIČIUS (Vilnius Gediminas Technical University, Technological Sciences, Environmental Engineering – 04T).

The dissertation will be defended at the public meeting of the Council of Scientific Field of Environmental Engineering in the Senate Hall of Vilnius Gediminas Technical University at 1 p. m. on 27 January 2012. Address: Saulėtekio al. 11, LT-10223 Vilnius, Lithuania. Tel.: +370 5 274 4952, +370 5 274 4956; fax +370 5 270 0112; e-mail: doktor@vgtu.lt The summary of the doctoral dissertation was distributed on 23 December 2011. A copy of the doctoral dissertation is available for review at the Library of Vilnius Gediminas Technical University (Saulėtekio al. 14, LT-10223 Vilnius, Lithuania).

© Eglė Zuokaitė, 2011

VILNIAUS GEDIMINO TECHNIKOS UNIVERSITETAS

Eglė ZUOKAITĖ

KOMPOSTUOJAMO NUOTEKŲ DUMBLO TYRIMAI IR DUJINIŲ EMISIJŲ MAŽINIMO BŪDAI DAKTARO DISERTACIJOS SANTRAUKA TECHNOLOGIJOS MOKSLAI, APLINKOS INŽINERIJA IR KRAŠTOTVARKA (04T)

Vilnius 2011

Disertacija rengta 2007–2011 metais Vilniaus Gedimino technikos universitete. Mokslinis vadovas

doc. dr. Aušra ZIGMONTIENĖ (Vilniaus Gedimino technikos universitetas, technologijos mokslai, aplinkos inžinerija ir kraštotvarka – 04T).

Konsultantas doc. dr. Dainius PALIULIS (Vilniaus Gedimino technikos universitetas, technologijos mokslai, aplinkos inžinerija ir kraštotvarka – 04T).

Disertacija ginama Vilniaus Gedimino technikos universiteto Aplinkos inžinerijos ir kraštotvarkos mokslo krypties taryboje: Pirmininkas

prof. habil. dr. Pranas BALTRĖNAS (Vilniaus Gedimino technikos universitetas, technologijos mokslai, aplinkos inžinerija ir kraštotvarka – 04T).

Nariai: doc. dr. Paulius KERPAUSKAS (Aleksandro Stulginskio universitetas, aplinkos inžinerija ir kraštotvarka – 04T), doc. dr. Mindaugas RIMEIKA (Vilniaus Gedimino technikos universitetas, technologijos mokslai, aplinkos inžinerija ir kraštotvarka – 04T), prof. habil. dr. Petras VAITIEKŪNAS (Vilniaus Gedimino technikos universitetas, technologijos mokslai, aplinkos inžinerija ir kraštotvarka – 04T), prof. habil. dr. Vytenis Albertas ZABUKAS (Klaipėdos universitetas, technologijos mokslai, aplinkos inžinerija ir kraštotvarka – 04T).

Oponentai: dr. Nijolė KAZLAUSKIENĖ (Gamtos tyrimų centras, biomedicinos mokslai, ekologija ir aplinkotyra – 03B), prof. dr. Saulius VASAREVIČIUS (Vilniaus Gedimino technikos universitetas, technologijos mokslai, aplinkos inžinerija ir kraštotvarka – 04T).

Disertacija bus ginama viešame Aplinkos inžinerijos ir kraštotvarkos mokslo krypties tarybos posėdyje 2012 m. sausio 27 d. 13 val. Vilniaus Gedimino technikos universiteto senato posėdžių salėje. Adresas: Saulėtekio al. 11, LT-10223 Vilnius, Lietuva. Tel.: (8 5) 274 4952, (8 5) 274 4956; faksas (8 5) 270 0112; el. paštas doktor@vgtu.lt Disertacijos santrauka išsiuntinėta 2011 m. gruodžio 23 d. Disertaciją galima peržiūrėti Vilniaus Gedimino technikos universiteto bibliotekoje (Saulėtekio al. 14, LT-10223 Vilnius, Lietuva). VGTU leidyklos „Technika“ 1972-M mokslo literatūros knyga.

© Eglė Zuokaitė, 2011

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Introduction

Formulation of the problem Sewage sludge is classified as a category of biodegradable waste that

menaces to the environment and its component if handled improperly. Sewage sludge can be a source of biological and chemical pollution. Heavy metals accumulated inside it can pollute the soil, ground water. Unstabilized sludge contains agents of zymotic diseases that spread by means of insects or rodents. However, after the assessment of sludge property and proper treatment, the sludge becomes a valuable raw material that can be used in agriculture, energy use and so on.

Currently, handling and disposal of sewage sludge is still a global problem; and effective and, at the same time, inexpensive ways are being sought for its solution.

The processing of sewage sludge by some or other means faces the problem of release of gaseous emissions, and especially with chemical compounds of bad odour. Unpleasant smell is the alarm about the potential risk to the environment or human health. Because of gaseous state of contaminants and their capability to spread in the air easily, this problem is difficult to be dealt with. Harmfulness of odors gets their negative effects on human health. It is need to search simple, natural, safe sludge treatment technologies for the environment. Technologies should be based on biological processes occurring in nature dealing with sewage sludge treatment and odor emissions problem, and to maintain the presence of nutrients.

Topicality of the work Handling, processing and using of sewage sludge is a topical problem not

only in Lithuania but also in other parts of the world. Tighter environmental requirements stimulate to install more modern and efficient technologies for wastewater treatment. This increases the formation of sludge amount, the handling of which using current means starts to endanger the environment, does not meet long-term public interests anymore and contradicts the principles of sustainable development. One of the sludge treatment methods is composting, which helps to stabilize the sludge, reduces its amount, improves sludge structure and microbiological-parasitological indicators.

Various properties of sewage sludge in Lithuania have been examined by the scientists of Lithuanian Institute of Ecology led by prof. I. Eitminavičiūtė for many years. Survival and reproduction of worms grown in sewage sludge compost has been examined. Biological processes in re-cultivated sewage sludge dumps and the soil in the making by monitoring the changes of micro-

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organisms and abundance of microarthropods as well as their complex structure, and peculiarities of soil formation and its environmental state have been researched. Impact of sorption properties of sorbent ZeoVit on the changes of nitrogen compounds, heavy metals and biological activity in sewage sludge. Researches of ecotoxicological properties on the soil fertilized by sewage sludge have been carried out as well.

Scour and alkaline stabilization of sewage sludge has been studied by the scientists of Lithuanian Agricultural University. The process of composting of sewage sludge with wood chips was studied by the scientists Epstein and Willson. Swedish researchers Writter and Lopez-Real examined nitrogen losses and ammonia emissions from composted sewage sludge.

Composting of open type is known and applied in the world when not only an unpleasant odour is emitted in the environment, but also gases causing greenhouse effect. Proper handling of sewage sludge (biodegradable waste) has been particularly important recently because the products of decomposition have a significant impact on the process of climate change. Therefore, cheap and effective techniques for the reduction of emission of gaseous pollutants released during the composting process, using natural (natural) materials are relevant currently.

The object of research The objects of the research work are composting sewage sludge, gaseous

emissions and composting coverings. The aim of the work The aim is to examine the emissions of gaseous pollutants emitted during

the composting of municipal sewage sludge, to evaluate and identify effective means and tools which can be used for the reduction of organic and inorganic concentrations of gaseous pollutants released during the process of composting.

The tasks of the work

1. To examine the emission of gaseous pollutants released during the composting of sewage sludge, to analyse and identify regularity of the formation process of gaseous pollutants.

2. To determine the amounts of organic carbon in sewage sludge, to assess the decrease and trends in sludge composted in different ways.

3. To study main qualitative characteristics of sewage sludge before and after composting.

4. On the basis of experimental data, to find dependences between the parameters of sewage sludge composting and odour emissions.

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Methodology of researches The methodology for the research of gaseous pollutants emitted during the

process of sewage sludge composting; the methodology for the determination of organic carbon; the methodology for the identification of concentrations of nitrogen (N) and heavy metals has been used; ADMS 4 software package has been used in the work for the modelling of the dissemination of odour emissions.

Scientific novelty of the work Complex researches on the emission of gaseous pollutants during the

process of sewage sludge composting through the application of reduction measures of natural odours in order to determine their possibilities of usability and performance.

Practical significance of work results Based on results of research conducted can be assessed patterns of the

gaseous emissions through composting of sewage sludge. Designed cover for natural composting can be used to odors and gas emissions reduction and improving the quality of compost.

Propositions to be defended

1. After the creation of optimal conditions for sewage sludge composting (C:N, aeration, pH, temperature and humidity), and the use of wood waste during the process, it is possible to manage the emissions of gaseous pollutants emitted.

2. The coverage of the sewage sludge under compost with different fractions of wood waste (sawdust, shavings, shredded branches and chipped tree bark) helps to reduce pollution emissions (NH3, H2S, VOC), but the most effective coverage of wood waste is tree bark.

3. Compost which is covered with natural grass cover during the composting has less loss of organic carbon and nitrogen.

4. If composting cover created of two layers is used (shredded tree bark and soil with a layer of herbaceous vegetation), the gaseous emissions (NH3, H2S, VOC) can be effectively reduced and an unpleasant odour can be avoided at the same time.

Structure of dissertation The dissertation consists of an introduction, 6 chapters, conclusions, list of

references, and list of author’s publications. The total scope of dissertation is 155 pages, 12 numbered formulas, 79 illustrations, 11 tables and 204 references.

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1. The analysis of treatment and usage of sewage sludge and environmental pollution

The chapter deals with the generation of sewage sludge, its physical and chemical properties. Methods and technology for the treatment of sewage sludge are described. Mechanisms for the process of composting, conditions, factors and management of composting, technology for composting, indicators determining the properties and quality of a compost (product) and the possibilities of the use of sewage sludge has been analysed. Methods for the analysis of odours resulting from the processing and treatment of sewage sludge, and technologies and means applied for the reduction of gaseous pollution emitted during the process of composting have been described. 2. Investigations of gaseous pollutants released during composting sewage sludge

The following chapter provides methods for the examination of gaseous pollutants and odours emitted during the composting of sewage sludge, as well as the results of experimental tests and their analysis.

During the decomposition of organic (vegetative and animal origin) materials, not only gas of an unpleasant odour (sulphuric and nitrogen compounds of organic and inorganic origin, acids, aldehydes and ketones) is emitted, but also gases causing greenhouse effect (CO2, CH4, N2O). If optimal conditions for the composting have been created and additives have been used, it would be possible to reduce emissions of gaseous pollutants in the environment.

The aim of the research is to assess the regularity of formation of gaseous pollutants (NH3, H2S, VOC, CH4) emitted in the environment during the process of sewage sludge composting, and the possibilities for the reduction of those emissions through the application of natural additives (bark, sawdust, chips, small branches, zeolite, peat).

Experimental tests have been carried out in five stages: • During the first stage, the research of the composting of sewage sludge of 0.5 kg was carried out under laboratory conditions, which was covered or mixed with natural zeolite and peat. The composting facility was sealed with 4-liter casings 24 hours before taking gaseous samples. NH3, CH4 emissions were examined.

• During the second stage, the research of the composting of sewage sludge of 5 kg covered with wood waste (bark, sawdust, chips, small branches) was carried out under laboratory conditions. The compost was sealed in 45 l

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containers 24 before taking gaseous samples. NH3, H2S, VOC, and CH4 emissions were examined.

• During the third stage, the research of composting in sludge piles with artificial aeration was carried out under laboratory conditions. 15 kg of sewage sludge mixed with 1.5 kg of sawdust covered with compost covers (layer of grass, tree bark and grass layers, a layer of peat, peat and grass layers, sawdust and grass layers). Composting was done in sealed containers of 250 l. Samples of gaseous substances were taken 1 hour after the aeration in containers of 45 l 24 hours before sampling. NH3, H2S, CO2, O2, CH4 and VOC emissions were examined.

• During the fourth stage, the research of composting in piles was carried out under natural field conditions. 25 kg of sewage sludge mixed with 1 kg of sawdust and covered with compost cover (tree bark and grass layers, peat and grass layers, sawdust and grass layers). Instantaneous samples of gaseous emissions were taken by covering piles of compost with the casing of 45 l (dimensions: 590 x 390 x 290 mm). NH3 and VOC emissions were examined.

• During the fifth stage, the research of smells released during the composting of sewage sludge was carried out under natural field conditions. Sewage sludge and structural composting material was used for the examination of smells (wood and green waste). Natural aeration is in process during the mixing of compost piles every 7 days. Composted material is piled as follows: width – 4–5 m, height – 2 m, length (50, 80, 100 m). Instantaneous samples of smell emissions were taken by covering piles of compost with the casing (dimensions: 1000 x 500 x 750 mm). Smell emissions were examined.

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% . Sewage sludge

Sewage sludgecovered with peat

Sewage sludgecovered withzeolite

Fig. 1. Emission of methane gases during the composting of sewage sludge

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In the first stage, after the research of methane amounts which are emitted during the composting of sewage sludge, different trends are noticeable in the samples with the sludge and sludge coated with zeolite or peat layer. The largest amounts of methane are released from the uncoated sewage sludge. Emission of methane gases in % is shown in figure 1.

The results obtained indicate that the sludge covered with a layer of peat emits less methane. Even smaller amounts of methane are released from the sludge covered with a layer of zeolite. Analysis of the results shows that it can be assumed that the zeolite is an appropriate measure for the reduction of amount of gaseous pollutants (methane) released during the composting of sludge. Under anaerobic conditions, methane is released from the composted sewage sludge under the influence of bacteria. At the end of the phase of acetogenesis, the process of methanogenesis starts:

2.5 CH3COO- + 2.5 H+ → 2.5 CO2 + 2.5 CH4 (1)

During the process of methanogenesis, organic acids are dissociated to

CO2 and CH4. The second stage showed that it is efficient to use bark and sawdust for

the reduction of the emission of sulphuretted hydrogen (by covering or mixing) (Fig. 2). When sawdust is being used, concentration of sulphuretted hydrogen is reduced by 4–5 times, and on about 48th day of experiment, “zero” concentration is recorded.

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Sewage sludge

Sewage sludgecovered with sawdust

Sewage sludge mixedup with sawdust

Fig. 2. Emission of sulphuretted hydrogen during the digesting of sewage sludge During the third stage, when the experiment on the composting of

sewage sludge was carried out, it was found that sewage sludge coated with different covers emitted from 0.14 to 8.73 g/kg of NH3 within 80 days (Fig. 3).

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Non-covered

Covered with a grass layer

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Covered with sawdust ant agrass layer

Fig. 3. Ammonia gas emissions from the compost covered with covers of composting The largest content of ammonia were released during the composting of

sewage sludge mixed with sawdust (10:1), when it is uncovered – 8.74 g/kg of NH3. After composted material was covered with the peat layer, amount of released ammonia emissions decreased almost by three times, and reached 3.03 g/kg of NH3. When composted material was covered with grass layer, content of released ammonia emissions was 1.79 g/kg of NH3. Content of ammonia emissions was reduced most effectively by using the composting material of two layers: sawdust and grass layer – 0.29 g/kg of NH3, peat and grass layer – 0.19 g/kg of NH3, tree bark and grass layer – 0.14 g/kg of NH3. On the fifteenth day of the experiment, the highest ammonia concentration of 575 mg/m3 was recorded in sewage sludge composted with sawdust, uncoated with compost cover, which is lower by 18% compared with ammonia concentrations (700 mg NH3/m3 ) recorded by other authors (Haug) from digesting facility for sewage sludge.

The fourth stage. During the anaerobic process, volatile organic compounds are as an intermediate product of reactions in process. Different levels of VOCs emitted during the composting of sewage sludge are shown in figure 4. According to complete composting mechanism, it is difficult to control VOC emissions into the environment because they are practically all different during the process of composting as an intermediate product. In addition, these are compounds of different composition.

The following data shows that the maximum amount of VOCs emissions were on 8 and 24 day of composting, from uncovered compost. The largest concentration of VOC was determined during the composting of sewage sludge mixed with sawdust on 24 day of the experiment, and it was 64.8 mg/m3.

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Fig. 4. VOC emissions from sewage sludge under compost An average of 28.5 mg/m3 of VOC was released from uncovered compost

piles, having covered them with bark and grass layer – 9.26 mg/m3, having covered with the layer of sawdust and grass – 10.31 mg/m3, and having covered with peat and grass layer – 14.10 mg / m3.

If compost cover composed of peat and grass layer is used, ammonia emissions decrease by 2 times on the average. If the compost cover composed of sawdust and grass layer is used, ammonia emissions decrease by 2.8 times on the average. VOC emissions into the environment is reduced the most efficiently by the layer of bark and grass, even by 3.1-fold.

During the fifth stage, the measurements of odour emissions form sewage sludge and composted sewage sludge with additives using the method of dynamic olfactometry were carried out (Fig. 5). Emissions released from sewage sludge compost, from materials (compost) composted at a different time, that is – for 4, 5, 8, 12, 18, 26, 33, 39, 43 and 54 days. The ambient air temperature during the research was +14°C.

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Fig. 5. Emission of odours during the composting of sewage sludge

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Research of air samples taken from the compost piles using the method of dynamic olfactometry was carried. Marginal value of maximum allowable concentration of odour in the air of living environment in Lithuania is 8 European odour units (8 OUE/m3).

It was found that during the first days of composting, the concentration of unpleasant odours increases with the release of emissions, the peak concentration of 992 OUE/m3 was determined in composted pile of sewage sludge on 8 day. During the biochemical decomposition of organic substances in an aerobic environment, the proteins in compost resolve into CO2, H2O, H2S, NH3 and emit the heat. The assessment of concentrations of odour and individual chemical compounds determined by the research during the composting of sewage sludge shows that odour concentrations of sewage sludge composted for 8 days are conditioned by the release of H2S. Odour emissions in sewage sludge composted for 12 days decrease because of reduction of H2S emissions. Odour emission in sewage sludge composted for 18 and 33 days reaches peak again; it can be justified by the maximum release of NH3. During the complete process of composting, as a by-product, there is a flash of VOC emissions which increase the odour emissions.

Fixed concentrations of odours from compost and sewage sludge can be compared with the concentrations of odour emissions released by the municipal waste dump: newly piled waste – 1200 OUE/m3, temporarily covered waste – 240 OUE/m3, permanently covered waste – 120 OUE/m3. Odour emission of 1400 OUE/m3 was determined from the “fresh” sewage sludge, similar concentrations is released from the stack of newly piled municipal waste – 1200 OUE/m3. Odour concentration of 1048 OUE/m3 was indicated in the premises for sewage sludge thickening. 3. Investigations of main qualitative characteristics of sewage sludge and compost

Currently, in the world, great attention is paid at the relationship between the soil and climate changes. Soil fertility depends most on organic substances of the soil. None the less is also important that these substances are the second largest source of carbon after the oceans. It is necessary not only to protect natural sources of carbon, but also to expand them.

Under ideal aerobic conditions, organic substances are resolved to CO2 and H2O. During the composting in an aerobic environment, 50% of organic carbon is removed from the compost in the form of CO2. During the composting under anaerobic conditions, during methane emission (CH4), losses of carbon are up to 95%.

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Organic carbon was determined using analyzer for combined carbon of solid sample module SSM-5000A of series Shimadzu TOV-V.

Carbon losses during the composting are calculated according to the formula:

Carbon loss = initial mass of С – final mass of C x 100 (2)

initial mass of C Experimental researches have shown that the greatest carbon losses (Table

1) are during the composting of uncovered sewage sludge with sawdust. The research data showed that during the composting of sewage sludge with peat and grass layer, losses of organic carbon amount to 13.7%. Main losses of carbon occur in active phase, during which micro-organisms rapidly dissociate biodegradable substances. Table 1. Losses of organic carbon (C) composting in piles under field conditions Type of sample Losses of organic carbon (C), %

after 2 weeks after 4 weeks after 6 weeks Sewage sludge with sawdust 10.7 15.0 15.5 Sewage sludge with sawdust, covered with layer of bark and grass 6.5 10.5 12.1 Sewage sludge with sawdust, covered with layer of peat and grass 8.1 12.1 13.7 Sewage sludge with sawdust, covered with layer of sawdust and grass 5.0 8.9 10.5

During the composting process of biodegradable waste, when waste wood

of different fractions (bark, sawdust, shavings, branches), peat and zeolite was used (by mixing and covering), emissions of gaseous pollutants containing carbon can be stopped.

Sewage sludge can be used as a fertilizer in agriculture if the amount of heavy metals (Cd, Cu, Ni, Pb, Zn, Cr, Hg) does not exceed allowable concentrations (EEC 86/278).

Content of compound nitrogen in sewage sludge ranges from 2.2 to 5.3% in a dry substance, and includes ammonia, nitrites, nitrates, carbamate and organic nitrogen. During the composting of biodegradable substances, nitrogen loss is mainly due to the emissions of NH3, but also gaseous N2, NO3 and N2O can be released. Kjeldahl nitrogen is a content of organic nitrogen and ammonia nitrogen in the sample determined after mineralization. It does not include nitrites, nitrate nitrogen, and does not necessarily include all organic nitrogen.

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The research was carried out by composting of sewage sludge mixed with wood sawdust uncovered and covered with various natural covers (bark and grass layer, sawdust and grass layer, peat and grass layer, grass layer, peat). Every ten days, the samples were taken and analysis of nitrogen was analyzed, the experiment was carried out in 60 days (Fig. 6).

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Covered with a bark andgrass layerCovered with a sawdustand grass layerCovered with a grass layer

Covered with peat

Covered with peat and agrass layerNon-covered

Fig. 6. Concentration of Kjeldahl nitrogen during the composting of sewage sludge covered with natural covers

For the research of heavy metals, sludge dewatered with centrifuge from wastewater treatment plants of Vilnius city was used. This sludge was used for composting experiments. Heavy metals determined: Cu, Pb, Zn, Ni, Cr, Cd (Fig. 7).

0200400600

Concentration, mg/kg 130 34,8 390 30,7 40 2,33Cu Pb Zn Ni Cr Cd

Fig. 7. Content of heavy metals in sewage sludge Content of heavy metals in sludge determines the final disposal method or

use of sludge. Content of heavy metals in sewage sludge used in agriculture is strictly regulated by the legislation of the EU and other countries. Contents of heavy metals Cu, Zn, Cr found in sludge of wastewater treatment plants of Vilnius city exceed the permissible levels, therefore it is forbidden to use it in agriculture.

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4. Mathematical modelling of odour dispersion released during composting process

ADMS numerical model is practical, short-range dispersion model that

simulates the results of wide radius, and passively releases it into the atmosphere both singly and in combination with other pollutants.

Modelling of odour dispersion in ambient air has been performed, from the compost piles of sewage sludge by assessing odour intensity in odour units (OUE) during the composting process. Modelling of odour dispersion was carried out from non-composted sewage sludge, and composted sewage sludge with additives – for 4, 8, 18, 26, 33, 39 and 54 days. Data of odour measurements were used in mathematical model. Odour dispersion was simulated at small wind – 1 m/s, at the average predominant wind in Vilnius city – 3.5 m/s, when speed of wind was at 10 m/s. The direction of wind is important in determining toward where the pollutants are going to be taken. The stronger the wind speed is, the lower concentrations of pollutants are, especially if the sources of pollution are close to the ground surface or their height is low.

Marginal value of maximum allowable concentration of odour in the air of the living environment in Lithuania is 8 European odour units (8 OUE/m3) (HN 121:2010). If the odour concentration in air is 5 OUE/m3, a weak odour may be felt.

Modelling of odour dispersion was conducted from sewage sludge with additives composted for 8 days (Fig. 8) showed that if wind speed is 1 m/s, the odour downwind from compost pile will be felt 165 meters away. With wind speed at 10 m/s, the odour of sewage sludge composted for 8 days will be felt 70 meters away, downwind from the pile.

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Fig. 8. Odour dispersion from sewage sludge composted for 8 days Compared the results of odour dispersion modelling from the non-composted

sewage sludge with additives composted for 8 days, it is seen that when sewage

v =1m/s v = 10 m/s

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sludge is being composted, mainly CO2 is emitted into the environment, which does not affect the odour, thus odour emissions released are reduced, and also the distance from the pile decreases where the unpleasant odour is felt. 5. Engineering solutions

If composting is carried out in closed facilities, it is important to ensure the

release of gas emission. For this purpose, compost covers of a variety of materials and compositions are used. The main aim of composting covers is associated with solution concerning the air pollution and odour issues.

Patent application No 2011 082 was prepared and presented (2011) under the chapter topic. Title of invention – compost cover.

Fig. 9. Scheme of composting coverings: 1 – sewage sludge and/or other waste under compost, 2 – layer of composting gas retention and cleaning composed of shredded tree bark (8–10 cm), 3 – textile, 4 – peat/soil layer (3–5 cm) with herbaceous vegetation The principle of effect of composting cover. Material under compost

(sewage sludge and other structural materials) are piled up or put in a tunnel-type composting facilities with active (perforated pipes with air injection system) or passive aeration. Compost surface is covered with the layers of composting covers of natural materials. The inner layers of composting cover surface (2, 4) consist of bark and peat/soil, which not only keep the heat, but also gases released during the composting. The upper layer of plants accelerates sludge (biodegradable waste) humification. Through the nitrification process, the plants assimilate nitrogen, thus the emission of nitrogen compounds into the environment is reduced, and the excess level of nitrogen in sludge is decreased as well. If CO2 concentration increases, photosynthetic activity of plants and biomass production is also increased, total amount of assimilated carbon grows therefore emission of carbon dioxide formed during the composting into the environment is reduced. Plant root system creates an extra aeration of compost pile.

General conclusions 1. The analysis of the literature showed that selection of sewage sludge

treatment technologies focused on reducing the quantity of sludge and

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its use, but not fully explored the possibility of natural remedies to prevent the problems of odours and the gaseous emissions released into the environment.

2. The research of sewage sludge composting under aerobic conditions showed that from sewage sludge with different coated in a period of 80 days NH3 split from 0.14 to 8.73 g/kg. The largest quantity of ammonia eliminate from composted sewage sludge mixed with sawdust (10:1), when it uncovered – 8.74 g/kg of NH3. The effect of the 40–50 mm peat layer of composted materials evolved ammonia emissions decreased almost three times and reached 3.03 g/kg of NH3. 3. During the experiment under field conditions showed that ammonia emissions from compost piles the most efficient, even 3.6 times decrease upper layer of peat (40–50 mm) and grass (40–50 mm). The most efficient volatile organic compounds emissions to the environment and reduces the bark layer of grass, even 3.1 times.

4. Under field conditions composted sewage sludge with additives reduces odour emissions 4 times (up to 352 OUE/m3) compared to not process the sewage sludge, odour emissions, which OUE/m3 to 1400.

5. The research data showed that the composting of sewage sludge coated with peat, compost organic carbon losses amounted only to 4.6%, while the effect of the composting of sewage sludge and sawdust with a layer of grass, organic carbon loss during the 6 weeks was 10.5%.

6. Research has shown that more nitrogen stays in sewage sludge which is covered with layer of tree bark and grass neither in uncovered sewage sludge. The initial nitrogen content 3.89%, after 60 composting days decreased to 2.99%.

7. Result of mathematical modelling of odours dispersion showed that when wind speed is 3.5 m/s odour is feeling 65 m downwind from 4 days composted sewage sludge with additives and from untreated sewage sludge – 155 m away.

8. After covering composted sewage sludge with natural coatings, consisting of a layer of grass and tree bark or sawdust layer, reduced emissions, as well as compost lose less nitrogen and carbon. Composting cover reduces the release of ammonia 98.4%, volatile organic compounds – 72%.

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List of published works on the topic of the dissertation In the reviewed scientific periodical journals Zigmontienė, A.; Zuokaitė, E. 2010. Investigation into Emissions of Gaseous Pollutants during Sewage Sludge Composting with Wood Waste. Journal of Environmental Engineering and Landscape Management. Vilnius: Technika. ISSN 1648-6897. 18(2): 128–136 (Thomson ISI Web of Science). IF = 1,508 (2009). Zuokaitė, E.; Zigmontienė, A. 2010. Organinės anglies tyrimai nuotekų dumble ir komposte. Mokslas – Lietuvos ateitis = Science – future of Lithuania: Aplinkos apsaugos inžinerija. Vilnius: Technika. ISSN 2029-2341 print / ISSN 2029-2252 online 2(2): 119–124 (Index Copernicus). Zuokaitė, E.; Zigmontienė, A. 2009. Amoniako ir metano dujų, išsiskiriančių kompostuojant nuotekų dumblą, tyrimai. „Mokslas – Lietuvos ateitis“ Aplinkos inžinerija. Vilnius: Technika. 110–113 (Index Copernicus). Zuokaitė, E.; Ščupakas, D. 2007a. Utilization of sewage sludge from acid casein produc-tion for soil fertilization. Journal of Environmental Engineering and Landscape Management. 15(3): 166–172 (Thomson ISI Master Jornal List). In the other editions Zigmontienė, A.; Zuokaitė, E. 2011. Research of organic carbon loss in sewage sludge compost by using composting covers. 8th International conference “Environmental engineering“: selected papers, May 19–20, 2011 Vilnius, Lithuania. Vilnius: Technika, ISBN 2029-7106. 1: 503–507. Zuokaitė, E.; Zigmontienė, A. 2011. Dujinių emisijų kompostuojant nuotekų dumblą kaupuose tyrimai. Aplinkos apsaugos inžinerija. 14-osios Lietuvos jaunųjų mokslininkų konferencijos „Mokslas – Lietuvos ateitis“, straipsnių rinkinys (2011 m. balandžio 14 d.). Vilnius: Technika. 29–33. Zigmontiene, A.; Zuokaite, E. 2008. Efficiency optimisation of sewage sludge usage for soil fertilisation. The 7th International Conference. Environmental Engineering 1: 472–477. (Thomson ISI Proceedings). Zuokaitė, E.; Zigmontienė, A. 2008. Nuotekų dumblo tvarkymas ir kvapų mažinimo problema. [CD], Aplinkos apsaugos inžinerija. 11-osios Lietuvos jaunųjų mokslininkų konferencijos „Mokslas – Lietuvos ateitis“ pranešimų medžiaga. Vilnius: Technika. 542–552. Zuokaitė, E.; Ščupakas, D. 2007b. Rūgštinio kazeino gamybos nuotekų dumblo panau-dojimas maistinių augalų tręšimui. Aplinkos apsaugos inžinerija. 10-osios Lietuvos jaunųjų mokslininkų konferencija „Mokslas – Lietuvos ateitis“. Vilnius: Technika. 237–244.

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Prepared application of patent Zigmontienė, A.; Zuokaitė, E. Kompostavimo danga. Nr. 2011 082.

About the author Eglė Zuokaitė was born in Pakruojis district on 18 October 1979. In 2005, she

acquired bachelor's degree in environmental and occupational safety at Faculty of Technology at Šiauliai University. In 2007, she received a master's degree in environmental engineering at the Faculty of Environmental Engineering at Vilnius Gediminas Technical University. Since 2007 – she is a graduate student at Vilnius Gediminas Technical University. Currently, she is working as an assistant and consultant at the Department of Environmental Protection at Vilnius Gediminas Technical University, and a researcher at the Institute of Environmental Protection. KOMPOSTUOJAMO NUOTEKŲ DUMBLO TYRIMAI IR DUJINIŲ EMISIJŲ MAŽINIMO BŪDAI

Problemos formulavimas Nuotekų dumblas priskiriamas biologiškai skaidžių atliekų kategorijai, kuris, netinkamai tvarkomas kelia pavojų aplinkai ir jos komponentams. Nuotekų dumblas gali būti biologinės ir cheminės taršos šaltinis. Jame sukaupti sunkieji metalai gali teršti dirvožemį, gruntinį vandenį. Nestabilizuotame dumble yra užkrečiamųjų ligų sukėlėjų, kuriuos platina vabzdžiai ir graužikai. Tačiau, įvertinus dumblo savybes ir tinkamai pasirinkus jo tvarkymo būdus, dumblas tampa vertinga žaliava, kurią galima panaudoti žemės ūkyje, energetinėms reikmėms ir kt.

Nuotekų dumblo tvarkymas, jo nukenksminimas šiuo metu vis dar globali problema, ir jos sprendimui ieškoma efektyvių, o tuo pačiu ir nebrangių būdų.

Vienais ar kitais būdais apdorojant nuotekų dumblą susiduriama su išsiskiriančių dujinių emisijų, o ypač nemalonų kvapą turinčių cheminių junginių problema. Nemalonus kvapas – tai signalas apie galimą pavojų aplinkai ar žmogaus sveikatai. Dėl teršalų dujinio būvio ir jų savybės lengvai sklisti ore, ši problema sunkiai sprendžiama. Kvapų kenksmingumas pasireiškia jų neigiamu poveikiu žmogaus sveikatai. Sprendžiant nuotekų dumblo tvarkymo ir išsiskiriančių kvapų problemą, bei norint išsaugoti jame esančias maistines medžiagas, reikia ieškoti paprastos, natūralios, saugios gamtinei aplinkai dumblo apdorojimo technologijos, paremtos biologiniais procesais, vykstančiais gamtoje.

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Darbo aktualumas Nuotekų dumblo tvarkymas, apdorojimas ir panaudojimas – aktuali

problema ne tik Lietuvoje, bet ir kitose pasaulio šalyse. Griežtėjantys aplinkosauginiai reikalavimai skatina diegti modernias ir efektyvias nuotekų valymo technologijas. Dėl to didėja susidarančio dumblo kiekiai, kurių tvarkymas iki šiol naudojamais būdais pradeda kelti grėsmę aplinkai, nebeatitinka ilgalaikių visuomenės interesų, prieštarauja darnios plėtros principams. Vienas iš dumblo apdorojimo būdų – kompostavimas, kurio dėka pasiekiama dumblo stabilizacija, sumažinamas jo kiekis, pagerinama dumblo struktūra ir mikrobiologiniai-parazitologiniai rodikliai.

Lietuvoje įvairias nuotekų dumblo savybes eilę metų tyrė Lietuvos ekologijos instituto mokslininkai, kuriems vadovavo prof. I. Eitminavičiūtė. Tirtas sliekų, auginamų nuotekų dumblo komposte, išgyvenimas ir reprodukcija. Ištirti rekultivuotų nuotekų dumblu sąvartynų, besiformuojančių dirvožemių biologiniai procesai, stebint mikroorganizmų ir mikroartropodų gausumo bei jų kompleksų struktūros pokyčius, bei dirvožemio formavimosi ypatumai ir jo ekologinė būklė. Tirtas sorbento ZeoVit sorbcinių savybių poveikis azoto junginių, sunkiųjų metalų ir biologinio aktyvumo pokyčiams nuotekų dumble. Buvo atliekami dirvožemių, tręštų nuotekų dumblu, ekotoksikologinių savybių tyrimai.

Nuotekų dumblo išplovimą ir šarminį stabilizavimą tyrė Lietuvos žemės ūkio universiteto mokslininkai. Mokslininkų Epstein ir Willson tirtas nuotekų dumblo kompostavimo su medžio drožlėmis procesas. Švedų mokslininkai Writter ir Lopez-Real tyrė azoto nuostolius ir amoniako išsiskyrimą iš kompostuojamo nuotekų dumblo.

Pasaulyje žinomos ir taikomos atviro tipo kompostavimo technologijos kai į aplinką išsiskiria ne tik nemalonaus kvapo, bet ir šiltnamio efektą sukeliančios dujos. Tinkamas nuotekų dumblo (biologiškai skaidžių atliekų) tvarkymas pastaruoju metu ypač svarbus, nes irimo produktai daro žymų poveikį klimato kaitos procesui. Todėl šiuo metu aktualūs pigūs ir efektyvūs kompostavimo proceso metu išsiskiriančių dujinių teršalų mažinimo būdai, naudojant natūralias (gamtines) medžiagas.

Tyrimų objektas Darbo tyrimų objektas – kompostuojamas nuotekų dumblas, dujinės

emisijos ir kompostavimo dangos.

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Darbo tikslas Darbo tikslas – ištirti dujinių teršalų emisijas, išsiskiriančias

kompostuojant komunalinių nuotekų dumblą, įvertinti ir nustatyti efektyvius būdus ir priemones, kuriomis galima mažinti kompostavimo procese išsiskiriančių dujinių organinių ir neorganinių teršalų koncentracijas.

Darbo uždaviniai 1. Ištirti dujinių teršalų emisijas, išsiskiriančias kompostuojant nuotekų

dumblą, išanalizuoti ir nustatyti dujinių teršalų susidarymo proceso dėsningumus.

2. Nustatyti organinės anglies nuotekų dumble kiekius, įvertinti jos sumažėjimo ir kitimo tendencijas skirtingais būdais kompostuojamame dumble.

3. Ištirti pagrindines kokybines nuotekų dumblo charakteristikas prieš ir po kompostavimo.

4. Eksperimentinių duomenų pagrindu rasti priklausomybes tarp nuotekų dumblo kompostavimo parametrų ir kvapų emisijų.

Tyrimų metodika Darbe taikytos dujinių teršalų, išsiskiriančių kompostuojant nuotekų

dumblą, tyrimų metodikos; organinės anglies nustatymo metodika; azoto (N) ir sunkiųjų metalų koncentracijos nustatymo metodikos; išsiskiriančių kvapų sklaidai modeliuoti naudotas ADMS 4 programinės įrangos paketas.

Darbo mokslinis naujumas Kompleksiniai nuotekų dumblo kompostavimo proceso metu išsiskiriančių

dujinių teršalų tyrimai taikant natūralias kvapų mažinimo priemones, siekiant nustatyti jų naudojimo galimybes ir efektyvumą.

Darbo rezultatų praktinė reikšmė Remiantis atliktų tyrimų rezultatais galima įvertinti dujinių emisijų

dėsningumus kompostuojant nuotekų dumblą. Sukurta natūrali kompostavimo danga gali būti naudojama kvapo ir dujinių emisijų mažinimui bei komposto kokybės pagerinimui.

Ginamieji teiginiai 1. Sudarius optimalias nuotekų dumblo kompostavimo sąlygas (C:N,

aeravimas, pH, temperatūra ir drėgmė), ir, proceso metu naudojant

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medienos atliekas, galima valdyti išsiskiriančių dujinių teršalų emisijas.

2. Padengus kompostuojamą nuotekų dumblą skirtingų frakcijų medienos atliekomis (pjuvenos, drožlės, smulkintos šakos ir smulkinta medžių žievė) sumažėja teršalų emisijos (NH3, H2S, LOJ), tačiau efektyviausia danga iš medienos atliekų – medžio žievė.

3. Kompostas, kuris kompostavimo metu padengiamas natūralia žoline danga, praranda mažiau organinės anglies ir azoto.

4. Naudojant sukurtą dviejų sluoksnių (smulkinta medžio žievė ir dirvožemio sluoksnis su žoline augalija) kompostavimo dangą, galima efektyviai sumažinti dujines emisijas (NH3, H2S, LOJ), tuo pačiu išvengti nemalonaus kvapo.

Disertacijos struktūra Disertaciją sudaro įvadas, šeši skyriai ir rezultatų apibendrinimas. Darbo

apimtis yra 155 puslapiai, panaudota 12 numeruotų formulių, 79 paveikslai, 11 lentelių ir 204 literatūros šaltiniai.

Bendrosios išvados 1. Išanalizavus mokslinę literatūrą nustatyta, kad, parenkant nuotekų

dumblo tvarkymo technologijas, didžiausias dėmesys skiriamas dumblo kiekio mažinimui ir jo panaudojimui, tačiau nepilnai ištirtos galimybės kaip natūralių priemonių dėka išvengti kvapų ir kitų dujinių emisijų išsiskyrimo į aplinką problemos.

2. Atlikus nuotekų dumblo kompostavimo tyrimus aerobinėse sąlygose nustatyta, kad iš skirtingomis dangomis padengto nuotekų dumblo 80 parų laikotarpyje, išsiskiria nuo 0,14 iki 8,73 g/kg NH3. Didžiausi amoniako kiekiai – 8,74 g/kg, išsiskiria kompostuojant nepadengtą nuotekų dumblą, sumaišytą su pjuvenomis (10:1). Padengus kompostuojamas medžiagas 40–50 mm durpių sluoksniu, išsiskiriančio amoniako kiekis sumažėja beveik tris kartus, ir siekia 3,03 g/kg NH3. 3. Eksperimento, atlikto lauko sąlygomis, metu nustatyta, kad amoniako išsiskyrimą iš komposto efektyviausiai, net 3,6 karto sumažina durpių (40–50 mm) ir žolės (40–50 mm) sluoksnis. Efektyviausiai, net 3,1 karto lakiųjų organinių junginių išsiskyrimą į aplinką sumažina žievės ir žolės sluoksnis.

4. Lauko sąlygomis kompostuojamo nuotekų dumblo su priedais kvapų emisija sumažėja 4 kartus (iki 352 OUE/m3), lyginant su neapdoroto nuotekų dumblo kvapų emisijomis, kurios siekia 1400 OUE/m3.

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5. Tyrimų duomenys parodė, kad, kompostuojant nuotekų dumblą padengtą durpėmis, organinės anglies nuostoliai komposte tesiekė 4,6 %, o kompostuojamą nuotekų dumblą padengus pjuvenų ir žolės sluoksniu, organinės anglies nuostoliai per 6 savaites siekia 10,5 %.

6. Tyrimų metu nustatyta, kad padengus nuotekų dumblą medžio žievės ir žolės sluoksniu, daugiau azoto lieka komposte, nei nepadengtame. Pradinis azoto kiekis 3,89 %, per 60 kompostavimo parų sumažėjo iki 2,99 %.

7. Atlikus kvapų sklaidos matematinį modeliavimą, nustatyta, kad esant vėjo greičiui 3,5 m/s nuo 4 paras kompostuoto nuotekų dumblo su priedais pavėjui kvapas jaučiamas 65 m atstumu, o nuo neapdoroto nuotekų dumblo – 155 m atstumu.

8. Kompostuojamą nuotekų dumblą padengus natūraliomis dangomis, sudarytomis iš žolės sluoksnio bei medžių žievės ar pjuvenų sluoksnio, sumažėja teršalų emisijos, taip pat kompostas praranda mažiau azoto ir anglies. Siūlomos kompostavimo dangos amoniako išsiskyrimą sumažina 98,4 %, lakiųjų organinių junginių – 72 %.

Trumpos žinios apie autorių Eglė Zuokaitė gimė 1979 m. spalio 18 d. Pakruojo rajone. 2005 m. įgijo

aplinkos ir profesinės saugos bakalauro laipsnį Šiaulių universiteto Technologijos fakultete. 2007 m. įgijo aplinkos inžinerijos mokslo magistro laipsnį Vilniaus Gedimino technikos universiteto Aplinkos inžinerijos fakultete. Nuo 2007 m. – Vilniaus Gedimino technikos universiteto doktorantė. Šiuo metu dirba asistente ir konsultante Vilniaus Gedimino technikos universiteto Aplinkos apsaugos katedroje bei tyrėja Aplinkos apsaugos institute.