SEARCHING FOR RENEW ABLE ENERGY SOURCES ON URBAN AREAS

The possibilities and capacities of energy production from renewable sources in urban areas were studied on the example of the city of Kharkiv, Ukraine (population ca. 1.4 mln, occupied 2 area ca. 320 km ). The following alternate renewable sources and ways for energy production (except solar and wind) have been identified: (1) biogas to be produced at municipal landfills; (2) biogas to be produced from sewage sludge accumulated at wastewater treatment plants; (3) wood wastes from urban dwellings' reconstruction and furniture renewal; (4) litter from tree stands of the city (woody and leaf litter, debris, dead wood, etc.); (5) biomass harvested while the phytotechnologies are applied for brown field remediation (energy crops, willows and poplars, etc.). The energy potential of primary and secondary renewable energy sources has been estimated. Approach to decision-making on optimal allocation of sites for decentralised energy production on the city's territory and relevant technologies for energy production are discussed.


I INTRODUCTION
Increasing demand for energy is a modern civilization's "trademark". In global and regional energy consumption cities take major part while global urban population is steadily growing. Increased demand and supply of energy is nowadays accompanied with drastically increased prices for energy from non-renewable sources and simultaneous depletion of such sources. Ensuring energy security and urban and regional development sustainability implies searching for both renewable sources and ways to improve energy efficiency (3,6,9,15,18]. The European Union's energy policy targeted at increase of a share of total energy production in EU countries from renewable sources to 20% by year 20 I 0. The target will be achieved through introduction of the Intelligent Energy concept, supporting technological innovations 1 and broad public campaigns • In the transition and developing countries whose economies are much dependent on exported energy sources national policies' development is generally taking similar direction although being less articulated. Ukraine is among such countries, and today its economy is based to the Biomass produced by an urban ecosystem has potential value as a primary renewable source of energy. This nom,ally includes woody and leaf litter, debris, dead wood and timber from the urban forestry, and hay harvested from numerous urban lawns and road verges. By practices of Ukrainian municipalities such biomass is treated as an organic waste and, instead of energy production, it is directed to landfills during summer and autumn seasons every year. Not long ago it was even burnt in urban streets and yards in the open air, but nowadays such a practice is strictly prohibited by national sanitary regulations. In contrast to Ukraine and NIS countries, in many European cities technology schemes were adopted to utilise urban forestry litter and harvested biomass for the purposes of energy production. In Poland, a new EU Member state, there are more than I 00 000 boilers utilising energy from the burning wood biomass [ I 8]. At the same time, a team from Ukrainian Research Institute of Technical Heat Physics (ITHP, Kyiv, Ukraine) developed the method and device for biomass processing, which allows obtaining solid fuel (charcoal) and combustible gas as final products. Charcoal can be further used for electricity production as well as for heat supply in steam-heating boiler [ 15]. Charcoal production is mentioned by British specialists as one of economic benefits of urban forestry [2]. An alternative way of biomass treatment is thermal decomposition and subsequent conversion of synthesised gas to liquid hydrocarbons. This technology of special bio-fuels production for future drive concepts using Fischer-Tropsch synthesis was developed at the already mentioned CUTEC-Institute GmbH.
With increased application of phytoremediation systems to contaminated land rehabilitation in industrial and urban areas worldwide the biomass produced by such systems can also be harvested and utilised for the purposes of energy production by means of technological solutions as described above.
The last but not least to mention is a growing in recent years practice of energy crops (either annual or perennial herbaceous species) and energy wood plantations that may be introduced in urban or peri-urban areas. Brown fields and like lands suit such a purpose that a number of studies in the United Kingdom and Scandinavian countries, among others, confirmed (2, 1 1].

Although utilisation of the primary and secondary renewable energy sources in contemporary
Ukraine is yet insufficiently understood and at the very preliminary stage, the urgent needs of national security in the energy field call for concrete practical actions. We made an attempt to show in this paper the prospects and opportunities for and possible benefits from incorporation of renewable energy sources that long have been associated with wastes only, on the example of the country's second largest city, Kharkiv. This study by no means provides for ready-to-use solutions and rather aims at raising awareness of municipal professionals, decision-makers and prospective investors to the problem outlined.

The city profile
The city of Kharkiv founded in 165 1-1654 grew from a small fortress, a frontier town to the second largest city in the nation, the biggest regional centre, and the former capital of Ukraine ( 19e 19-1934). It is located in the northeast part of country on rolling plain of the southeast fringe of the Forest-steppe zone of East Europe. Nowadays, Kharkiv is a central city for the region (Ob last) named after it. By the time of collapse of the Soviet Union the city of Kharkiv was a leading centre of education, research and technological development (especially in defence-related fields), culture, transportation with remarkable industries (machinery, aircraft, turbine, power, electric and transportation engineering). Decline of typical city of industrial era became a characteristic sign in Ukraine during the last 15 years, and the city of Kharkiv has not been an exception. Under conditions of transition economy the city's profile has significantly changed. After several years of strong economic decline some revitalization of industrial activities occurred in recent years, and the city's economy shows stable growth from 200 I. However, at the same time its population decreased almost by I 0% since 1990 when it reached its maximum, 1.6 min. Recent census gave a figure of I 466 300 inhabitants living in the city. Total city's area is ca. 320 km 2 , of which almost 2 10 km 2 are built-up lands and about 140 km 2 are occupied by urban forest (4]. About ¾ of total number of city's residents occupy multi-storied dwellings, and the rest inhabit private low-storied ones. Total energy supply of the city of Knarkiv ranged 88 450 GJ/year (2003, (4]), of which 26% was supplied by a local thermal power station TEC-5, 16% -by another local thermal power station, TEC-3, and the rest -by municipal heat generating company "Kharkiv Heating Networks". Main fuel used for centralized energy supply is methane gas extracted from the largest region's gas fields, "Shebelynske". Local energy strategy has been developed with relevance to national energy regulations, namely the Energy Efficiency Act of Ukraine ( 1994) and a number of presidential and governmental decrees ( 1994-2000). It is a part of a regional Integrated Programme of Energy Efficiency for 2003-20 IO developed by Regional State Administration and approved by Regional Council. Energy efficiency goals are stated in annual plans and programmes of socio-economic development of the city of Kharkiv. Nevertheless, energy consumption and supply have increased by 23% since 2000 without significant improvement of energy efficiency.  Sewage sludge generated at I min m l per year at two wastewater works of the Municipal Enterprise of Sewerage and Wastewater Treatment, "Kharkivkomunochystvod", is treated and stored at drying fields that occupy about 120 ha of lands in the southern part of the city, near the settlement of Bezlyudivka. With application of advanced mechanical treatment since 2005, the sludge volume is significantly reduced as well as the area needed for sludge drying, In the future about 100 ha of existing fields will be reclaimed by the municipality, and application of phytoremediation measures is therefore expected, In our study, this area is considered for growing energy crops and woods, 2 The Ordzhonikidzevski municipal district (area 33.4 km ) with its industries and residential areas separated from the fom1er with boulevards, greenways and parks served a good model area for estimation of amounts of biomass produced by the urban forestry and harvested on open public spaces. Today, tree stands occupy 936 ha, open public space -4 ha, Middle-aged trees (40-60 years) take the majority of total tree stands where Poplars (Populus deltoides, P. balsamifera, P, x berolinensis), Mapples (Acer negundo, A, platanoides), Lime-trees (Tilia cordata, T x europaea, T platyphyllos), Ash (Fraxinus excelsior, F lanceolata, F americana) and Common Birch (Belli/a pendula) predominate,

Sources of information and methods
For estimation of amount of biogas that may be obtained from city's landfills and data on solid wastes accumulation on the urban area, technical reports of the Research and Design Institutes of Municipal Engineering ("KharkivKomunNDIProject") and Advanced Technologies for Municipal Economy ("UkrKomunNDIProgres"), as well as annual reports (2001e-2005) of the Kharkiv City Council were used, Amount of biogas, which may be extracted from the landfill, was estimated as the following [7]: V BG =M SW , C OM , (Iz), cun.d,gc. '1. (I) where V8c -amount of biogas, me 3 ; Mswtotal amount of solid wastes accumulated at a landfill, kg; CoM -content of easily digestible organic matter (normally equals 0, 5-0,e7); zcoefficient of ash content of organic matter (normally equals 0, 2-0,3); C an digesr -degree of anaerobic digestion (nom1ally equals 0A-0,5), me 3 /kg, Data on waste composition and, specifically, share of wood fractures in total amount of solid wastes were obtained from two monographs written by local professionals [I, 9], Total amount of wood wastes generated from the city's dwellings was estimated according to the

Municipal landfills as a source of biogas
Following the data on actual amounts of municipal solid wastes accumulated and stored at two operated and one closed landfills and excluding wood wastes from the calculation the amount of potential biogas yield was estimated using fomrnla (e I), We put the coefficient of biogas utilisation as 50%, and, at the heating value of 20 MJ/m ofbiogas, we estimated total potential energy output from using this renewable secondary source in the city of Kharkiv ( Table I ).  Comparing estimated potential energy output from landfill biogas that could be generated at 2 existing sites we found that it is compatible to ¼ of total annual energy consumption of the city. If we consider the annual rate of solid wastes accumulation in the city, and sound technology would be implemented to produce, collect and utilise biogas for energy production it would count to almost 5% of total annual urban energy supply.

Municipal sewage sludge as a source of energy
Recent measurements of heating value of sewage sludge from the treatment fields of the Municipal Enterprise of Sewerage and Wastewater Treatment, "Kharkivkomunochystvod", showed average figure of 21 MJ/kg of dried sludge with organic matter contents of 19%. With annual generation of I · I 0 6 m 3 , municipal sludge makes good potential secondary renewable energy source for the city. More detailed investigations on the technologies of its utilisation for the purpose of energy production and feasibility study are needed that will give correct estimation of this source's contribution to total urban energy supply in the future.

Wood wastes
The contents of wood and cardboard in all municipal solid wastes of the city of Kharkiv are 2.8% and 5% by volume, respectively. In large waste fractions contents of wood reach 66-75%, and share of large fractions in total solid wastes is approximately I 0% by volume [I]. We estimated total amount of solid wastes based on the Standards for solid waste 3 accumulation in settlements of Ukraine as 0.15 m per year per person living in multi-storied residential houses, and 0.22 m 3 per year per person living in low-storied dwellings. Taking total urban population at 1.4 min residents and assuming the ratio of residents of the fom1er category to the later category as 3: I we estimated amount of solid wastes generated at each kind of residential dwellings. Then, total mass of wood wastes was estimated at average wood for oaks [ 19]). For energy output estimations we used heating value of wood wastes as 19 MJ/kg. The results are shown in Table 2.  source of renewable energy would count up to 8% (0. 7 I 0 MJ ) of total annual energy demand/supply of the city.

Litter from urban tree stands
Litter kg/m we got 7.8 · 10 kg of leaf biomass. Usually only a half of leaf litter is removed out tree plots in average (from I 00% on streets and boulevards to only 5-10% in dense forest-like 6 stands), so biomass available for further utilisation is about 4.0 · l 0 kg. Multiplying by IO we got a rough estimate of total available urban leaf litter. Further utilisation of this primary renewable source -either for composting or biogas/energy production purposes -will be justified as a result of feasibility study of relevant technologies introduction to the municipal economy. At the moment we could suggest that this source of energy would count only for 1.0 -1.5% of total energy demand/supply of the city.
In addition to tree wastes in the model area, small amount of harvested biomass came from mowing the lawns at open public spaces (4 ha) and from removal of almost 42 000 annually planted flowers at the end of vegetation season. For the later, harvested biomass was

Biomass produced with applied phytoremediation systems
Although phytoremediation measures were not yet applied in the city of Kharkiv at the scale larger than 0.e1 ha, these are seen as a prospective source of biomass for additional alternate energy production. In the nearest years in the future phytoremediation systems may be applied at the existing municipal sewage sludge drying fields on the area of 100 ha. We recommend that 60 ha of this area to be planted with energy willow and poplar plantations with a short rotation period of 3 years, when average shout height reaches 4-6 m. Then every year a 1/3 of the planted area, i.e. 20 ha, might be harvested and replanted with new shouts. From published data [ 1 1], dry biomass is estimated as I 0-15 t/ha, totally 200-300 t per year. Its utilisation might result in almost 3.6 -5.4 · I 0 6 MJ of energy annually from one relatively small plot.

CONCLU SIONS
Our preliminary study found that in the city of Kharkiv there is a plenty of still unused primary and secondary renewable energy sources: solid wastes and landfill leachate rich of organic matter; municipal sewage sludge; large fractions of wood wastes that should be treated separately from total municipal solid wastes; urban tree and leaf litter; biomass of herbaceous plants harvested from open public spaces (lawns, road verges, etc.).
Rough estimation of total energy output that could be obtained at simultaneous utilisation of biogas and biomass gave a figure of 15-20% of total annual energy supply in the city of Kharkiv from these renewable energy sources only. In present, however, these sources are not utilised at all, and further investigations on technology efficiency and feasibility of biogas, energy and other possible benefits production, as well as on logistics of biomass collection points and small heating plants/facilities location are needed. It is certainly a decentralised solution to urban energy supply that complements existing centralised system. However, questions of what could be capacities of single facilities utilising different sources of renewable energy in the city, where should these be located, how many customers these would serve, and what are environmental impacts of such facilities still need to be addressed. A pilot scale application in the nearest future would provide for the information upon which decisions on full-scale implementation of technologies and facilities for renewable energy production and utilisation in the city of Kharkiv will be made.