In this research, we present a new methodology to indirectly assess the concentration levels of the biochemical oxygen demand (BOD) and total nitrogen (T-N) of dewatered cake by evaluating the amounts of the volatile solids (VS) and total solids (TS). Information regarding the BOD and T-N concentrations of dewatered cake could then be used to estimate the Greenhouse Gas (GHG) emissions caused by sewage treatment. To this end, regression equations were derived by considering the relationship between the product of two solid terms: (TS × VS) and BOD/T-N levels of digested sludge. The optimal regression equations for BOD and T-N were computed as y = 152425x (R2= 0.969, p < 0.05) and y = 128378x (R2= 0.970, p < 0.05), respectively. For the purposes of verification, the applicability of the regression equations was tested using the data for other periods not considered in the regression analysis. Accordingly, the differences between the measured and estimated concentration data (derived using the regression equations) were within the standard deviation of the measured concentrations. However, the concentrations estimated by regression equations were quite different from those obtained by conventional methods. Nonetheless, such differences did not significantly change GHG emissions, thus we conclude that the plant specific regression equations can be derived from the methods presented in this study, although more efforts are needed for its validation in various respects.

Aluminum can is one of the common and economically valuable recycling items in municipal waste streams. In this study, the reduction rate of the greenhouse gas emission and energy savings were estimated when aluminum cans are recycled by using material flow analysis, US EPA WARM method, and EU Prognos method. Based on the results, approximately 16,630 ton of aluminum in 2010 was recovered as ingot, while 10,873 ton of aluminum can to can recycling occurred in the same year. The reduction rate of aluminum recycling was estimated to be 240,986 tCO2eq/yr by US EPA WARM method, while about 305,283 tCO2eq/yr was found by the recycling using EU Prognos method. The difference resulted partly from the different system boundary and the loss rate during aluminum recycling process. The results of the energy savings and greenhouse gas reduction rate would be valuable for waste management policy makers to estimate the potential reduction rate of greenhouse gas by aluminum can recycling and accelerate recycling infrastructure of waste streams. This study also implies that the applications and results of both methods to estimate greenhouse gas reduction rates by aluminum can recycling should be carefully reviewed and acknowledged before the use of the method due to the different assumptions and results that are anticipated.

With a growing concern of greenhouse gas (GHG) emissions due to climate change, many activities and efforts onthe greenhouse gas reduction have been implemented in solid waste sectors. Since recycling is the major managementoption for solid waste in Korea, it is important to estimate the reduction of the greenhouse gas emission during recyclingprocesses. In this study, two common methodologies, Prognos method of EU and waste reduction model (WARM) methodof USA, have been critically reviewed and compared to estimate the reduction for recycling of waste paper in terms ofsystem boundary, recycling processes, and emission factors. As a common point of two methodologies, the reductionfactors for the paper recycling have been developed by subtracting the recycled product emissions from the virgin productemissions to get the greenhouse gas savings. While the recycling losses and transportation are considered in twomethodology development, there are a number of differences between the methodologies in system boundary,transportation distance and forest carbon sequestration. As a result, it caused the difference in final greenhouse gasreduction factor of paper recycling. The reduction factor was −820kgCO2eq/ton in Prognos method, while −3,891kgCO2eq/ton was found in the WARM method. When both methods were applied to recycling of waste paper in Korea,the greenhouse gas reductions by the Prognos method and the WARM method were found to be 3,485.2tCO2eq/day and2,248.8tCO2eq/day, respectively. When the carbon sequestration by forest is considered in the WARM method, thereduction rate was estimated to be 16,538.3tCO2eq/day. The main reasons for such difference can be attributed to systemboundary and forest carbon sequestration. Especially, forest carbon sequestration can be an important factor in Korea thatusually manufactures papers from imported pulp from abroad. This study implies that the applications and results of bothmethods to estimate greenhouse gas reduction by waste recycling should carefully reviewed and acknowledged beforeuse due to the different assumptions and results that are anticipated.