The Influence of Distance and Atmospheric Elements on the Concentration of Odour from Refuse Derived Fuel (RDF) Operations

Odour is an environmental element that occurs as varieties of aroma, either pleasant or otherwise to its immediate community. The various sources of odour pollution may come from either natural or of human activities. Odour concentration may change due to environmental factors such as atmosphere, topography, distance and mitigation efforts. This study describes a study on the influence of distance and athmospheric elements on concentration of odour generated by the Refuse Derived Fuel (RDF) operations. The distribution of odour concentration was measured using Odour concentration meter XP-329 III series per its distance from the RDF operations. The results indicated that distance factors did influence the odour concentration. Results at test stations of distances farther from the RDF showed incrementally higher distribution of odour concentration compared to those nearer to the RDF. In addition, athmosperic elements like temperatures, humidity, wind speed and directions also evidenlty linked to the distribution of odour concentration.


INTRODUCTION
Odour is an environmental component that can contribute to its changes. Odour pollution is an indicator of environmental change that impact health and human well-being. Studies on odour pollution could be viewed from two major parameters either objectively and subjectively (Zaini, 2012). Objective study involves analyses of concentration, intensity, endurance and odour character. While subjective analysis involves perceptions and human sensory pertaining to hedonic tone, nuisance, objectability and intensity.
In Malaysia, studies on odour pollution is still at an infancy stage. Most studies only revolved around issues and challenges of odour pollution (Othman et al., 2008) Specific study on measuring dumpsite odour concentration was first to have been conducted only in 2011. Series of such pioneering studies were conducted by Zaini et al. (2011a, b, c), Ahmad (2011), Lukman (2012, Zaini (2012) and Zaini et al. (2012a, b). In developed countries like in the EU, Japan, Australia and New Zealand, studies on odour pollution have reached a phase of excellence involving various aspects including perceptions (Laister, 2002), gas spread and odour (Struss, 2007;Casey et al., 2008), method of mesurement (Littaru, 2007;Davoli et al., 2003;Shi, 2004;Sironi et al., 2005Sironi et al., , 2007Zarra et al., 2008;Romano et al., 2007), impact of pollution on health and wellbeing (Wing et al., 2008), control and mitigation (Shui-Jen et al., 2003;Casey et al., 2006) and management.
Specifically this study is aimed to identify the distance factors in infuencing the distribution and concentration of odour emitted from the RDF operatons. In adddition, atmospheric elements such as temperatures, comparative humidity, wind direction and speed were also analysed to identify its collective effects on odour concentration. In addition to instrument-aided measurement of the odour concentration of each station per to their RDF distance; trangession analysis was also conducted to examine the relationship between odour concentration and athmospheric influence.

Materials and location of study:
This study was conducted on the RDF operation located in Semenyih, Kajang in the state of Selangor. The RDF was operated by Recycle Energy Sendirian Berhad (RESB) under the Kajang District Council. The RDF operation was capable to convert solid wastes into electric power. The RESB output of this source of renewable energy was to a maximum of 9 Megawatt (MW) through conversion of 700 tons of solid wastes daily.

Method of measuring odour concentration:
The instrument for measuring odor concentration was the Odour concentration meter XP-329 III series. The intensity of odour was recorded in odour unit concentration per cubic meter or ou/m 3 . The strength of odour concentration could be measured between 0 to 2000 ou/m 3 .

RESULTS AND DISCUSSION
Distance factor: Figure 1 indicates the relationship between distance and odour concentration. Even though the results indicated the R 2 = 0.046 is less than 0.5, almost approximating zero and the model used was rather weak, it could nevertheless explicate the relationship of distance per odour intensity whereby the farther the distance from the RDF the higher the distribution. Commonly, higher odour concentration was often detected at areas nearer to the source such as sewage treatment plants and dumpsites (Klein, 1999;Zaini, 2012). However the findings of this study indicated positive relationship between distance and odour, whereby the farther the distance the higher the odour were concentrated. Based on the analysis, the distribution of odour was higher at stations farther from the RDF. An instance, for stations with distance exceeding 800 m, higher concentration distribution was shown on normal days and after rains. The distribution of odour at distances farther from the RDF was due to the influence of the RDF tall funnels. The emission and distribution of smoke through the funnels aided by the wind factors caused the odour concentration to spread farther and higher. Stations 7 and 9 received higher concentration of odour. Both stations were at 1.2 km and 1.6 km from the RDF.

Temperature factor:
The environmental temperature is a meteorological component which influenced the concentration of an odour. Based on Fig. 2, the results of the regression analysis indicated R 2. values was weak at R 2 = 0.086. Despite the weak model to illustrate this relationship, the results of the study indicated the distribution of odour concentration was higher at stations with lower temperatures compared to those with higher ones. The distribution of odour after rains was found to be concentrated at stations with low temperatures around 25ºC (Fig. 2). This situation arises due to after rains effects, stable temperatures and wind speed.
Wind factor: Figure 3 shows the results of regression analysis which found the R 2 for wind variables and odour concentration to be weak at R 2 = 0.015. Despite a weak modelling to illustrate this relationship, it is nevertheless clarifying positive relationship for the variables under study. Fig. 3  of odour on normal days and after rains during the slow winds. The analysis clearly indicated higher odour concentration at slower wind velocity compared to higher ones. This phenomenon occured due to the temperature of the athmosphere being stable and collected at areas with high wind velocity. These findings are similar to Laister (2002) and Zaini (2012) who found higher wind velocity to be influential in the distribution of concentrated gas and odour. Figure 4 shows the influence of comparative humidity on distribution of odour concentration. Based on regression analysis, it was found, that there existed contrastive relationship between comparative humidity and the odour observed. Higher distribution of odour concentration was largely at observatory stations with higher humidity exceeding 80%.

CONCLUSION
Based on the findings, there were evidently variances in the average of odour concentrations between normal times and after rains. The average of the concentrations indicated highest readings in the evening and afternoon in both weathers. Nevertheless the average concentration of odour was found to be higher after rains.
Hence, the influence of distance and meteorological factors such as temperatures, wind and humidity were comparatively influential in the distribution of odour concentration from the RDF. Overall, despite the regression analysis indicating all factors with weak R 2 , less than 0.5; they were still capable of affecting positive relationships on the distribution of odour concentration.