ORGANIC WASTE ' S POTENTIAL AS RENEWABLE ENERGY AT SUPIT URANG LANDFILL IN MALANG CITY

This research are to know the correlation of the number of population with the amount of waste in Malang city and biogas potential at Supit Urang landfill. Then also counting the percentage of biogas which has been used as gas fuel by citizens around the landfill and as electrical energy potency. The average amount of waste in Malang city is 410,45 ton per day. Organic waste composition at Supit Urang landfill is 64,9% or in the average it’s about 137.989,57 kg per day. From that amount, the average of biogas which is produced is 19.146,57 m 3 per day or about 574.397,05 m 3 per month. Biogas utilization is for fuel gas by 408 houses near the location of that landfill, that’s about 18.385,19 m 3 per month or about 3,2%. Therefore that’s still has 96,8% biogas potential or about 556.011,86 m 3 per month which has not been utilized yet. That potency can produce electrical energy 2.613.255,75 kWh per month or 3,63 MW. If the average efficiency level of conversion from biogas to electricity is 35%, the electric potential become 914.639,51 kWh per month or as big as power station with energy 1,27 MW.


INTRODUCTION
Population growth will cause an increase in the amount of waste.If not anticipated with the right waste management, it will cause various problems.As the heaping of waste at landfill can cause environmental problems, that are vegetation damage, water pollution by leachate, air pollution by unpleasant odors, risk of asphyxiaton risk of explosion and combustion, and greenhouse gas emisisions (Popov, 2005in Abreu, et al, 2011).Greenhouse gas emissions like carbondioxide gas (CO 2 ) and methane gas (CH 4 ) emit to the atmosfer so can cause ozon layer getting thinner and thinner.Accordingly there will be an increase in the earth temperature known as global warming.
The main contributor to the greenhouse effect is methane emission from landfill (Scharff and Jacobs, 2006).Methane gas emission 21 times more dangerous than CO 2 emission (Czepiel, et al., 2003).Popov (2005) in Abreu, et al (2011) explained that CH 4 and CO 2 can be generated within 20 years, but their emissions can continue for 50 years or more.
Kyoto Protocol and Waste To Energy Program support each country and government to reduce greenhouse gas emission and utilize the waste as energy source.Therefore, waste management at landfill need to be done, one of that by using the biogas which are produced as renewable energy.This purpose is to prevent greenhouse gas emission and global warming and also reduce the using of source energy from fossil like petroleum and coal.
Global warming as environmental problem has happened at all part of the world.Greenhouse gas emission has a risk of causing global warming not only from waste heap, but also as the side effect from using fossil energy.The reserve of the source of fossil energy getting decrease, but renewable energy still have great potency as be seen at Table 1 Efforts on energy conversion need to be done by encouraging green energy as renewable energy from organic waste biomass.It aims at getting energy sustainability.Government is expected to have a program for conversion from petroleum fuel to gas fuel and from waste to energy to reach sustainable development.
In the year of 2013 and 2014, Malang City government get appreciation of Adipura Kencana because of the success on waste management programs like Malang Waste Bank and biogas utilization at Supit Urang landfill.Biogas from the landfill has been utilized by the citizens around the landfill location as energy source, that is, as gas fuel.
The purpose of this research are not only to know the correlation of the number of population with the amount of waste in Malang City and biogas potential at Supit Urang landfill, but also to count the percentage of biogas which has been used as gas fuel by citizens around the landfill and as electrical energy potency.

Biogas's Forming Process
Biogas is generated from anaerobic waste decomposition process.Chemical reaction on that process is: Abreu, dkk (2011), anaerobic process happened for 10 -50 days.Sudrajat (2006) explained that the anaerobic composting process on organic waste go through four steps, which are: a. Hydrolysis process In this process, there is a decomposition of polymer organic material to monomer which can easily leach and results in amino acid, volatile acid, glycerol, etc. Fat is described by lipolytic bacteria with lipase's enzyme, while carbohydrate is described by cellulotytic bacteria with cellulose enzyme, and protein is described by proteolytic bacteria with protease's enzyme.

b. Acydogenesis process
In this process, there is organic monomer decomposition becoming organic acids (as format acid, acetic, butirat, propionat, valeriat) and alcohol by acidogenic bacteria.Other results from that process are CO 2 , H 2 , and methanol.

c. Acetogenesis process
In this process, organic acid and alcohol is changed as acetate, format, methanol, CO 2 and H 2 by acetogenic bacteria

d. Metanogenesis process
In this process, acetate is changed as CH 4 , CO 2 , and H 2 O by metanogenic bacteria.Nearly about 70% methane are formed from acetates, whereas the other 30% are from format acid, CO 2 , and H 2 .

Biogas Potential Counting
The method to calculate energy for anaerobic digestion from organic waste are (Frear, et  Biogas which will be utilized as electrical energy must be treated to increase its quality and consequent energy efficiency.The stability of efficiency level can be reached by adding blower so that biogas flow can give an adequate energy (Pierpaoli and Diotallevi, 2007).Conversion of biogas to electrical energy has efficiency level 30-40% (Eurelectric, 2003).

MATERIALS AND METHODS
Methods of this research are mix methods between qualitative and quantitative method.The location of this research at Supit Urang landfill in Malang city.
Primary data collected with questionaire and secondary data from Hygiene and Urban Landscaping Department Malang City.Samples are used to calculate the percentage of biogas which is used as gas fuel by citizens around landfill and the biogas potential as electrical energy using slovin formula, that are: (4) where: n is sample measure N is population measure e is error The number of population around Supit Urang landfill which are using biogas as gas fuel are 408 houses from 5 region that are region 3, 4, 5, 7 and 8.With 10% error, sample measure is: Sample obtained with purposive stratified random sampling method of each region, that are: Source: analysis result The analysis to know the correlation between the number of population and the amount of waste in Malang city, then the amount of organic waste and biogas potential uses SPSS version 19.Biogas potential analysis to know the percentage of biogas which are used as gas fuel, and the percentage of biogas potency as electrical energy uses Microsoft Excell.

RESULT AND DISCUSSION Population Number and Waste Amount
Based on data from Statistics of Malang City, Malang City's population number 2013 is 840.800 with the average of growth rate per year is 0,81%.The average of waste amount in Malang City is 410,45 ton/year.Correlation between population number with waste amount is 0.892.This value is adequately high and significant with p-value of 0. The correlation between organic waste and biogas potential is 1.This value so high and significant with p-value of 0 as seen at Table 4.An increase in the number of population will cause an increase in the amount of waste.It happens because waste results from human life activity.Therefore, if the population number increase, waste amount also increase too.The increasing of organic waste cause greater biogas potential.It happens because biogas results from organic waste fermentation.Eddine and Salah (2012) stated that the composition of MSW is closely related to lifestyle of the residents and economic development.In general, the composition of MSW in Malang City with eleven major categories of waste was identified: organics, paper and cardboard, plastics, glass, metals, textile, rubber, bones, hazardous waste, inert, and residues that can be seen at Therefore, there's still available biogas potential of about 556.011,86 m 3 /month.That potential has not been utilized yet as is so big, that is about 96,8%.If that potential are used as electrical energy, with assumption 1 m 3 biogas has the same measure as 4.7 kWh, that biogas's potential can produce electrical energy as big as 2.613.255,75kWh/month or about 3,63 MW.If the average of efficiency level of conversion biogas to electricity is 35%, so the electric potential becomes 914.639,51 kWh per month or as big as power station with energy 1,27 MW.
Source: Statistics of Malang City and Hygiene and Urban Landscaping Department Malang City (2014) Fig. 1 Population number and waste amount Malang City Fig 2. /day or about 574.397,05 m 3 /month.In average, people utilizes biogas's stove up to 4,5 hours per day or 135,19 hours/month.If each 1 m3 biogas can be utilized to cook up to 3 hours therefore biogas need for one house is about 1The percentage of biogas's utilization as gas fuel by citizen is 3,2%.

Table 1 .
. Primer Energy Source inIndonesia (2005) . Methane is the main component from biogas.On hall temperature and standard pressure, this gas is colourless and does not have bad smell.This gas is inflammable.

Table 2 .
Biogas Conversion, and Using

Table 3 .
Sample Number in Each Region