LIFE CYCLE ASSESSMENT OF DOMESTIC WASTEWATER TREATMENT IN MEDAN CITY, INDONESIA

Medan City already has been having Waste Water Treatment Plant (WWTP) under PDAM Tirtanadi (North Sumatera Government) supervision, namely IPAL Cemara. IPAL Cemara is off-site sewerage system to treat domestic wastewater, includes black and grey water. IPAL Cemara has maximum capacity 60,000 m 3 /day, but recently, the number of treated households by IPAL Cemara is 18,396 households and the used capacity is less than 10,000 m 3 /day. This research analyses on operational phase of IPAL Cemara on environmental impacts, starts at wastewater influent from households and ending at release of wastewater effluent and disposal of dry sludge. The phase of reuse or recycle of effluent wastewater and dry sludge, and waste management are not included. Functional unit in this research is treatment of 7,171 m 3 wastewater per day for a year. The system boundary starts at wastewater influent and ends at release of wastewater effluent. The characterization factors are tracked based on CML Baseline 2001 and all of data processed by Microsoft Excel. For the result, got that Aerated Pond has removal efficiency of BOD and COD more than 70%, but on the other hand, it is the largest contributor to Climate Change impact because of diesel consumption (16.97%), the amount of CO 2 (4,95%), and N 2 O (4.26%) from biogenic emission, and electricity use (3.04%). The 65% reducing of TSS is occurred in UASB Reactor but UASB Reactor also as contributor for Climate Change impact (16.63%) and Photo-Oxidant Formation impact (29.34%) due to the highest production of CH 4 . Facultative Pond contributes 49% of Climate Change impact and 31% of Photo-Oxidant Formation impact because of the highest production of CH 4 . Based on normalized by impact category, Freshwater Ecotoxicity and Eutrophication is the largest environmental impact in a whole system of IPAL Cemara. Freshwater Ecotoxicity caused by 72% CS 2 at Release of Wastewater and Eutrophication caused by 41.25% of NH 3 and 39.60% of N. It is Align with the result of normalized by Life Cycle Stage, shows that the Release of Wastewater Effluent is the largest contributor to environment in a whole system of IPAL Cemara.


Introduction 1
Medan City where is the capital city of North Sumatera province is the 3 rd biggest city in Indonesia with the large area is 265.10 km 2 , consists of 2,210,624 inhabitants. The average density of Medan City is 8,338 person/ km 2 and the average household size is 4.35 people/ household. The population of Medan City always increases year by year and for along 15 recently years, the increasing reaches 16%.
The increasing of population will increase household consumption of water and directly impacted to increase domestic wastewater production (Prinajati, 2020). As we have known that around 80% water consumption becomes wastewater (www.iges.or.jp, accessed March 2017). Domestic wastewater disposal without adequate treatment causes water sources contamination for drinking water, ground water, and river water (Yustiani et.al, 2018). Rapidly increasing of population leads some environmental issues in Medan City and the 2 nd biggest issue is decreasing rivers quality (Book of Environmental Status of Medan City, 2015).
Since 1995, Medan City already has been having Waste Water Treatment Plant (WWTP) under PDAM Tirtanadi (North Sumatera Government) supervision, namely IPAL Cemara. IPAL Cemara is off-site sewerage system to treat domestic wastewater, includes black and grey water. IPAL Cemara covers some areas of Medan City and Deli Serdang Regency with total coverage areas are 520 Ha of Medan City and 150 Ha of Deli Serdang Regency. However, the coverage area is low, only 3.63% of domestic wastewater is treated by IPAL Cemara. Approximately, 96.37% of households in Medan City rely on on-site sewerage systems; those are septic tank or latrine pit for treating black water and open drainage for grey water.
Life Cycle Assessment (LCA) is technique for assessing the potential environmental aspects and potential aspects associated with a product or service, by: compiling an inventory of relevant inputs and outputs, evaluating the potential environmental impacts associated with those inputs and outputs, and interpreting results of the inventory and impact phases in relation to the objectives of the study (ISO 14040.  (Zang et. Al, 2010), LCA of Wastewater Treatment Plants in Ireland (Mcnamara et.al, 2016), Comprehensive Life Cycle Inventories of Alternative Wastewater Treatment Systems (Foley et. Al, 2010), and LCA of a Municipal Wastewater Treatment Plant: A Case Study in Suzhou, China (Li et. al, 2013).
The objectives of this research are to find the operational impact of IPAL Cemara on environment by a whole system and each life cycle stage and to establish LCA framework of IPAL Cemara that could use as baseline to conduct continuous improvement and further deeply analysis.

Research Methodology
This research analyses on operational phase of IPAL Cemara on environmental impacts, starts at wastewater influent from households and ending at release of wastewater effluent and disposal of dry sludge. The phase of reuse or recycle of effluent wastewater and dry sludge, and waste management are not included.

a. Goal and Scope
This research aim at analyses on operational stage of IPAL Cemara on environmental impacts for establishing LCA framework that could be used to further research such as continuous improvement of IPAL Cemara. The research's scope includes wastewater influent, treatment and maintenance, treated water release, and disposed dry sludge. Functional unit in this research is treatment of 7,171 m 3 wastewater per day for a year. The system boundary starts at wastewater influent and ends at release of wastewater effluent. Electricity for operating machine and pump, diesel as generator fuel, lubricant consumption for operating and maintaining machine and pump are included within the system boundaries. Biogenic emissions, treated wastewater effluent, and disposed dry sludge are also included within the system boundaries. By-product production such as large solids, rags, debris, sand, gravel, cinder from Screening and Grit Chamber, also sludge from Aerated Pond and Facultative Pond are calculated but the environmental impacts of them are not take account. Based on interview with IPAL Cemara staff, the estimation of lubricant spill is 3% of lubricant residue, 97% is collected well and given to third party.
b. Life Cycle Inventory (LCI) The LCI of this research is CML Baseline 2001 from Leiden University. Accordance with CML 2001 guidance, there are some required data of IPAL Cemara operational, such as electricity use of each pump and machine, diesel consumption as generator fuel of each and machine, the amount of CO 2, CH 4, and N 2 O as air emission from electricity use, diesel and lubricant consumption, biogenic emissions, the constituents of treated wastewater effluent as water emission and disposed dry sludge as soil emission, and the number production of byproducts. All of data in Life Cycle Inventory is collected based on the functional unit, which is treatment of 7,171 m 3 wastewater per day for a year.  (Brander, 2011).  The emission factor of sludge is 0.4 tonnes CO 2 -eq. (Australian National Greenhouse Accounts, 2015).  Formula for estimating fuel combustion of diesel (Australian National Greenhouse Accounts, 2015) : Whre Eij is the emission of gas type (j) , (carbon dioxide, methane or nitrous oxide, from fuel type (i) (CO 2 -e tonnes), Qi is the quantity of diesel (Kilolitres) combusted for stationary energy purposes, ECi is the energy content factor of diesel (Gigajoule per Kilolitre) for stationary energy purposes, ECi Diesel equal to 38.6 Gj/kL, EFijoxec is the emission factor for each gas type (j) (which includes the effect of an oxidation factor) for diesel (Kilograms CO2-eq. per gigajoule), EF CO 2 = 69.9, EF CH 4 = 0.1, EF N 2 O = 0.2.  Aerobic wastewater treatment systems produce primarily CO 2, whereas anaerobic systems produce a mixture of CH 4 and CO 2 . Following equations provide a general means of estimating the CO 2 and CH 4 emissions directly from any type of wastewater treatment process assuming all organic carbon removed from the wastewater is converted either CO 2 , CH 4, or new biomass ( RTI International, 2010).
Where CO 2 is CO 2 emission rate (MgCO 2 /hr), CH 4 is CH 4 emission rate (MgCH 4 /hr), 10 -6 is Units conversion factor (Mg/g), Q ww is wastewater influent flow rate (m 3 /hr), OD is Oxygen demand of influent wastewater to the biological treatment unit determined as either BOD 5 or COD (mg/L), Eff OD is Oxygen demand removal efficiency of the biological treatment unit, CF CO2 is Conversion factor for maximum CO 2 generation per unit of oxygen demand equal to 44/32 or 1.375 gCO 2 /g oxygen demand, CF CH4 is Conversion factor for maximum CH 4 generation per unit of oxygen demand equal to 16/32 or 0.5 gCH 4 /g oxygen demand, MCF WW is Methane correction factor for wastewater treatment unit, indicating the fraction of the influent oxygen demand that is converted in anaerobic condition in the wastewater treatment unit, CF is aerated treatment process equal to 0, MCF is anaerobic treatment process equal to 0.8, MCF facultative lagoon, deep ( 2 m deep) equal to 0.2, BG CH4 is Fraction of carbon as CH 4 in generated biogas (default is 0.65),  is Biomass yield (g C converted to biomass/g C consumed in the wastewater treatment process),  aerated treatment process equal to 0.65,  anaerobic treatment process equal to 0.1,  facultative lagoon, deep ( 2 m deep) equal to 0  The wastewater treatment process (aerobic, anaerobic, or combination of aerobic and anaerobic) will affect the magnitude of the N 2 O emissions. This equation using to estimate N 2 O emissions for both aerobic and anaerobic process using an average value for percent of influent TKN emitted as N 2 O (RTI International, 2010).

d. Normalization
Normalization is an optional step in LCA that aids in understanding the significance of the impact assessment results. Normalization is conducted by dividing the impact category results by a normalized value (EPA, 2014). Indonesia does not has normalization factor therefore this research use normalization factors of World 2010 (Sleeswijk, 2008).

Quality of Wastewater Effluent
The quality of wastewater effluent is below government standard quality which each parameter is reduced gradually process by process. All parameters have reduction efficiency 90% except fats, oil, and grease however its effluent value already below government standard quality.

Fig. 6. Actual Total Coliform Comparison to Government Standart Quality
Actual BOD and COD are highly reduced in Aerated Pond up to 74% and 73% respectively, TSS is reduced around 65% in UASB Reactor, Total Coliform is reduced extremely 99% in Skimming Tank, meanwhile Fats, Oil, and Grease and pH are stable reduced in each process even the beginning value (fats, oil, and grease of wastewater influent) is below government standard quality.

Life Cycle Inventory (LCI)
In this research, the LCI is conducted base on the functional unit, which is the treatment of 7,171 m 3 wastewater per day for a year. Flow rate of effluent wastewater is higher 49% than influent wastewater.

Analysis of Normalization Result for a Whole System of IPAL Cemara
According to the normalization result, the analysis of a whole system of IPAL Cemara is able to do. This is analysis of the normalized by impact category and another one is analysis of the normalized by life cycle stage.