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Physicochemical Analysis of Gas Flaring Impact on the Environment of Host Communities in the Niger-delta

Uyigue L*, Enujekwu F. M.

Department of Chemical Engineering, University of Port Harcourt, East-West Road, Choba, Port Harcourt, Nigeria

Abstract: This paper is focused on the application of physical, chemical and meteorological parameters to assessing the level of impacts on environments exposed to gas flaring. Three locations, P, Q and R, where gas flaring activities are ongoing in the Niger-Delta region of Nigeria were selected for this study. Another location (S) with no gas flaring activity was used as control. Soil, rain-water and air samples were collected from study locations for the purpose of analysis. The results from the physicochemical parameters measurements showed that pH of soil and rain-water samples collected at set radial distances of 20, 50 and 100 m from flare points were generally acidic, hence indicating the presence of acid rains and acid soils around the flare locations. Heavy metals (Cr, Cd, As, Pb, Zn, Fe etc.) contaminations of the soil and rain-water samples were also evident, and the distribution followed similar trends as that of pH. Air quality parameters (such as SO₂, NO₂, H₂S, CO, VOC, SPM etc.) also showed higher concentration at test distances near the flare point and lower values at distances farther away from flare point. Based on these findings, it was observed that no safe human activity can take place at radial distances < 2 km away from the flare point. This is adduced to the prevalent abnormal air temperature; poor air quality, soil and rain-water acidity which characterized the selected gas flare locations.

Keywords: gas flaring, physicochemical parameters, natural gas, pollution, impact analysis

Citation: Uyigue L, Enujekwu F. M., Physicochemical Analysis of Gas Flaring Impact on the Environment of Host Communities in the Niger-delta. Journal of Environment Pollution and Human Health, 5 (1). 22-29. January 2017. doi:10.12691/jephh-5-1-4

1. Introduction

Natural gas flaring is a process of burning unused hydrocarbon gases and releasing its products into the atmosphere. Greenhouse gases (i.e. CO₂, CH₄, NOx etc) which causes global warming or climate change normally forms major components of the gas flare products [1,2]. Other components of the gas flare products include wasteful energies, toxic gases and dangerous particulate matters. In Nigeria, gas flaring activity is high and it mainly takes place in the Niger-Delta region (Figure 1) [3,4].

Figure 1. Map of Niger-Delta region with highlights of gas flaring location [5]

Gas flaring sites are usually located at ground level, surrounded by thick Mangrove vegetation or on arable lands surrounded by host communities [6]. Typical gas flare operations are normally associated with huge flames emanating either from a flare pit or from a flare stack (Figure 2). Other components of flare stack assembly include burners and flow lines. It can be oriented vertically or horizontally.

Figure 2. Typical gas flaring operation site in the Niger-Delta region (NDES, 1996)

Apart from the fact that gas flaring activities in the Niger-Delta region is an economic wastage of natural resource to Nigeria, it does have serious environmental implications on the host communities. For example, NOx and SO₂ gases which are contained in gas flares reacts with water to form acidic compounds. This finding has implicated gas flaring as being responsible for the acid rain syndrome often experienced in the Niger Delta region [7].

The retardation of crops growth in the Niger-Delta region has also been attributed to numerous gas flaring activities by the oil companies. This is because, crops and vegetation located around gas flaring sites have been found to experience decrease in leaf chlorophyll and internodes length, as well as drying of leafs due to increased air and surface temperatures [8].

Based on recent studies, tested surface and ground water samples obtained from some gas flare locations in Warri, Delta state were found to contain heavy metals at concentrations above the World Health Organization (WHO) maximum permissible limits [9]. The reasons were adduced to the presence of metals and other substances in gas flare emissions.

In light of the above, it is obvious that environments exposed to natural gas flaring can be affected by pollution. The consequences will be that soil, water and air qualities of the affected environments will be impacted negatively, thereby causing hardships on the inhabitants [10,11,12,13].

Therefore, the focus of this study is on the impact of gas flaring activity on some selected locations (i.e. P, Q, R and S) in Ogba/Ndoni/Egbema local government area of Rivers State, which is one of the states in the Niger-Delta region. Locations P, Q and R, have gas flaring activities currently ongoing, while there is no gas flaring activity in location S. The physicochemical property data that will be obtained from soil, rain-water and air samples analysis of these locations (including meteorological data) will be used as basis for the impact analysis. The findings from this analysis will help protect the inhabitants and their livelihoods.

2. Materials and Method

2.1. Materials

The main materials used for this work were soil, water and air samples taken from the fields under this study. Also, apparatus used for collecting these samples are listed: Hand Auger, hand gloves, towel (for soil sampling), foil packs and black polyethylene bags (for soil samples and sediment collection), plastic container (for water sampling), masking tape. Global positioning system, GPS (for coordinate mapping), camera, coolers and ice packs, distilled water and brush (for decontamination of sampling equipment) and gas detector. Also, equipment used for meteorological parameter measurements are anemometer, humidity meter, thermometer, barometer, radiometer and smoke charts.

2.2. Collection of Sample

Test samples of soil and rain-water were collected from the study locations: P, Q and R where gas flaring activities were on going, while location S with no flaring activity was used as control. Three soil samples each were collected at different radial distances away from the point of flaring specifically at 20 m, 50 m, 100 m etc. With the aid of hand auger, soil samples were collected at different depths from a sampling point: 0 -15 cm and 15 -30 cm. The collected samples were carefully labelled and wrapped in aluminium foils and stored in black polyethylene bags for onward transfer to the laboratory. Also, a total of three rain-water samples were each collected from different sampling points by using plastic containers placed at platforms 1.3 to 1.5 m above ground level. The sampling points are radial distances away from the flaring point: 20 m, 50 m, 100 m, 500 m and 700 m. These rain-water samples were each collected in 2 L capacity of sterilized plastic bottles with cork which were appropriately labelled before being taken to the laboratory.

2.3. Preparation of Sample

The soil samples were air dried for 5 days, after which they were sieved with 2 mm stainless steel mesh to remove large stones and debris from its content, thereby making it to have particles size range < 2 mm. The soil samples were also vigorously mixed for uniformity and homogeneity and then stored at room temperature. The rain-water samples were measured into acid free sample bottles and were appropriately labelled.

2.4. Test of Samples from Locations

2.4.1. Soil Sample Test

Soil samples collected at the gas flaring locations were subjected to physical and chemical property tests from which properties such as temperature, pH, exchangeable cations and heavy metal content were measured.

Soil pH

ASTM 44972-01 standard was adopted. Multi-parameter Hannah pH meter (model 9811) was calibrated and used. A soil suspension was prepared by mixing 10.0 g of soil sample with 150.0 ml of distilled water which was then allowed to stand for 30 mins before the pH meter electrodes were carefully inserted while the pH readings were recorded from meter for all soil samples.

Soil exchangeable cations

2.5 g of wet soil sample was weighed into a 50 ml Erlenmeyer flask and 15 ml of extracting solution containing 1M NH₄OAc (or ammonium acetate), pH = 7.0 was pipette into it to form a mixture. The suspension was stirred for 10 mins before being filtered using a Whatman filter paper. An atomic absorption spectrometer (AAS) was used to determine the presence of Ca, Mg, K and Na in the extract samples.

Soil heavy metal content

Aqua regia was used for this test. In it, 1.0 g of each soil sample was contacted with 10 ml of concentrated HCl and Nitric acids mixture in the ratio 3:1 (i.e. 7.5 ml HCl and 2.5 ml of HNO₃). The mixture was swirled and kept in the fume cupboard. The samples were digested on hot plate stirrer at 60°C until the cessation of white fumes. After cooling for 10 mins, 10 ml of deionised water was added and filtered using separating filter paper. The filtrates were analyzed using atomic absorption spectrophotometer (AAS) by Buck scientific (model 210/211VGP). Heavy metal absorbances detected at various wavelengths were mainly for Fe, Zn, Cu, Ni, Cd, Pb and Mg.

2.4.2. Rain-water Sample Test

Collected rain-water samples were subjected to the following tests: temperature, pH, sulphate, nitrate, bicarbonate and heavy metal content using spectrophotometer and turbid meter.

pH

The pH of the rain-water samples was measured using the re-calibrated multi-parameter Hannah pH meter (model 9811).

Sulphate content

ASTM D516 was adopted. Barium chloride was used to form a turbid solution of barium sulphate indicating the presence of sulphate. The analysis was performed by adding powdered Sulferver-5 reagent to 50 ml of sample, while turbidity formed was measured with HACH DR 2500 spectrophotometer at 420 nm wavelengths. Sulphate concentration was determined by comparing absorbance reading with that of standard curve.

Bicarbonate content

The method of ASTM D1067 was adopted. This involves double indicator titration of a known volume of water sample with a standard acid using phenolphthalein and Methyl orange indicators.

Heavy metal content

Atomic absorption spectrophotometer (AAS) was used for the analysis, while APHA 3111B method was adopted. The direct aspiration of the rain-water sample into a nitrous oxide/acetylene flame was carried out, through which a light source emitting a narrow spectral line of characteristic energy was used to excite free atoms of metals of interest in the sample. The concentration of the excited metal atom was calculated by comparison with a standard curves for metals.

2.4.3. Air Quality Test

Air quality tests for gas flare locations includes chemical characteristics of rain-water samples collected, direct detection of gaseous emissions in air at both flare and control locations as well as the general meteorology of the study environments.

Gas emission: detection and measurement

An MSA Orion multi-gas detector was used to detect and measure quantities of the different gases emitted at flare locations. The detected gases are CO, NOX, SO₂, VOC, H₂S, CH₄, VOC and SPM. Prior to actual measurement, a background gas detection and measurement was conducted at radius of 10 km away from flare location. Thereafter, actual measurements were taken at 20, 50, 100, 500 and 700 m respectively.

Air meteorology

Wind velocity, wind direction, humidity, temperature, atmospheric Pressure, heat radiation and smoke density were the measured meteorological parameters. A multi-parameter anemometer (Krestel Extech model 45112) was used to determine both wind direction and velocity of the flare location. Other parameters were measured as follows: humidity by humidity meter, temperature by thermometer, pressure by barometer, heat radiation by radiometer and smoke density by Ringelmann and miniature smoke charts (BS 2742:1969).

3. Discussion of Results

The results obtained from this work are presented in the Tables and Figure. It consist mainly of data measured from experiments for the properties of soil, rain-water and air samples collected from the locations P, Q and R in the Niger-Delta region where gas flaring is presently ongoing, while results for location S is used as control. The reason is because it had no gas flaring activities. Subsections of this discussion will include gas flaring impacts on soil, rain-water and air characteristics as well as the overall effect on host environments.

3.1. Gas Flaring Impact on Soil Characteristics

The analytical results of soil samples collected from locations P, Q and R at defined distances from the flare point and depths are presented in Table 1 – Table 3, wherein about 16 parameters were measured and compared with the DPR compliance standards for both target and intervention values (Table 4). The soil parameters were observed to be generally affected by gas flaring emissions. Most noticeable are those of soil pH and heavy metal content. The pHs of soil samples were noticed to be generally acidic even at farther distances from gas flare point. Thus, at 20, 50 and 100 m away from flare point, soil pH for location P (at near surface, 0 – 15 cm) were 4.68, 5.8 and 6.2. Similar trends were repeated in the other locations.

Also evident in Table 1 – Table 3 is that the soil samples from the study locations (P, Q and R) are contaminated with heavy metals (i.e. Pb, Zn, Cr, Cd, Ni and Cu) in relative amount compared with DPR limit. The observed influence of space distribution on the heavy metal contents of soils from flare point in the study locations is a justification of the impact of gas flares on soil parameters. For instance, Cr content of location P soil (taken at near surface and at 20, 50 and 100 m away from gas flare stack) were 4.89, 3.051 and 1.51 mg/kg respectively. Thus, the variations noticed for heavy metal content of soil samples in the flare locations P, Q and R are also attributed to the change in soil sampling point distances from the gas flare point.

Therefore, factors such as distance of sample from source of flare, duration of flare and height of flare stack can absolutely affect the distribution (or spread) of soils physicochemical parameters in a gas flaring environments. These findings corroborate the work of Ubani and Onyejekwe [11] wherein soil pH values changed from acidic to near neutral as soil samples were collected some distances away from flare point.

Table 1. Physicochemical properties of soil sample taken 20 m away from gas flare point at locations P, Q and R

Table 2. Physicochemical properties of soil sample taken 50 m away from gas flare point at locations P, Q and R

Table 3. Physicochemical properties of soil sample taken 100 m away from gas flare point at locations P, Q and R

Table 4. Physicochemical properties of control soil sample taken from location S with no gas flaring activity

3.2. Gas Flaring Impact on Rain-water Characteristics

The results of rain-water sample characteristics for gas flare locations P and Q are shown in Table 5, while that of the control location S is shown in Table 6. From the results obtained locations P and Q, the pH of rain-water samples collected at 50 m and 200 m from gas flare point were generally acidic. This is because the pH values were 5.2 (at 50 m), 6.47 (at 200 m) and 5.57 (at 50 m), 6.71 (at 200 m) for locations P and Q respectively. Therefore, it is an indication that acid rains presence is evident in the flare locations. The pH values of 7.9 and 8.8 for control location S is a confirmation that gas flaring contributes to acid rain syndrome. These findings corroborates Sonibare and Akeredolu [7] and Onuoma et al. [12] in which both implicated gas flaring as the main cause of acid rains.

Trace concentrations (< 0.01 mg/l) of heavy metals (i.e. Ni, Pb, Hg, Zn, Cu, As and Fe) were evident in the rain-water samples collected at set distances of 50 and 200 m from gas flare point for both locations P and Q respectively (Table 5). The control location S also had clearance values of its heavy metals content. However, the heavy metal content of rain-water from locations P and Q is likely to increase as flaring persists. This assertion is supported by the report of Nwankwo and Ogagarue [9] wherein high level content of heavy metals were detected in surface and ground waters obtained from a gas flare location in Delta State, Nigeria.

Table 5. Physicochemical properties of rain-water samples collected from study locations P and Q at different radial distances from gas flare point

Table 6. Physicochemical properties of control rain-water sample collected from location S with no gas flaring activity

3.3. Gas Flaring Impact on Air Quality

Air quality parameters measured for this study includes concentration of SO₂, NO₂, H₂S, CO, VOC, SPM etc. The results obtained for test radial distances from gas flaring points (i.e. 20, 35, 50, 75, 100, 500 and 700 m) are shown in Table 7. For instance, SO₂, NO₂, CO concentrations at 20 m from flare point showed 26.9, 42.89 and 18.80 μg/m³ respectively, while at 700 m from flare point, SO₂, NO₂ and CO concentrations were each given as < 0.01 μg/m³. These values are indications of low air quality index (AQI) and high risk factor of contamination for the environment and human inhabitants around the flare locations as indicated. This finding is corroborated by NEPA [14] wherein air quality at Kingston metropolis (within 1 - 2 km radius from source) showed a high risk factor. Note however that the measured air quality parameters constitute mainly acid gases which can also seriously affect the pH value of soil and rain-water samples collected.

Table 7. Mean air quality and meteorological parameters for gas flaring plant locations P, Q and R

Table 8. Control air quality assessment for location S with no gas flaring activity

3.5. Overall Impact of Gas Flaring Activities on the Locations

The results of physicochemical parameters obtained for the soil, rain-water and air samples of the study locations P, Q and R showed that gas flaring activities in the area had impacted negatively on the inhabitants. From this study, it was observed that no meaningful human activity can take place in any of the gas flaring locations at radial distances < 2 km away from flare point. This is because of the high pollution loads imposed on these environments arising from increased pH of soil and acid rain concentrations (due to gas emissions), abnormal air temperature (due to flare radiation), heavy metal concentration and poor air quality due to flare emissions (particularly CO, NO₂, SO₂, smoke and particulate matter contents).

Consequently, the underlining effects of gas flaring on these locations and its inhabitants are numerous. Notable ones are poor soil fertility (due to soil pH, heavy metals and toxics pollution), health hazards (such as skin problems, cancer, reproductive health problems, respiratory disorders etc.), climate change (bringing about flooding) and economic loss (due to impediment of their traditional occupation, farming).These analyses agreed with Ajugwo [10] wherein broad-based consequences of gas flaring were enumerated.

4. Conclusion

This study has shown that gas flaring activities in the Niger-Delta region of Nigeria still impact negatively on the environments of its host communities. This inference was drawn from the results of the physicochemical analysis performed on soil, rain-water and air samples collected from the study locations. Evident from the physicochemical analysis are the increased pH and high concentrations of heavy metals in soil and rain-water samples collected at measured distances from gas flaring points. Also, detectable quantities of gaseous emissions were evident from the gas faring stacks, and abnormal air temperature and increased smoke density were observed for the different flare locations. These are strong indications that the study locations were affected by pollution. Even though most measured parameters from the study appeared permissible from a safer distance of more than 2 km from the flare point. With time, the concentrations are likely to build up in the host environments if the gas flaring activities persist.

Notation

AAS= Atomic Absorption Spectrophotometer

AGOC= Alexander's Gas and Oil Connections

APHA= American Public Health Association

AQI= Air Quality Index

ASTM= American Society for Test and Materials

BS= British Standard

DPR= Department of Petroleum Resources

FEPA= Federal Environmental Protection Agency

NDES= Niger Delta Environmental Survey

NEPA= National Environment and Planning Agency

SPM= Suspended Particulate Matter

VOC= Volatile Organic Compound

WHO= World Health Organization

WMO= World Meteorological Organization

References

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