THE CHALLENGES AND THE EFFECTS OF AGGREGATE SIZES ON THE CONCRETE STRENGTH

Abstract

Physico-chemical characterisation of industrial effluent is of importance in view of its inherent toxic substances. Effluent from cement plant located in Nigeria was characterised and its impact on the receiving Onyi River was investigated in this study. Effluent, water samples from upstream, discharge point along the river course and downstream location were collected monthly. The river was monitored up to about 1 km downstream from the discharge point for a period of twelve months. The impact of the effluent on the water quality downstream was shown by reduced dissolved oxygen. With respect to upstream, the levels of pH, nitrate, phosphate, total solid, total suspended solids, total dissolved solids, turbidity and biological oxygen demand at downstream were much high, arising from the influx of cement effluent. The cement effluent significantly contributed to the levels of Zn (0.045 ± 0.003 mg/L) and Pb (0.016 ± 0.001 mg/L) downstream such that they exceeded the criteria set by USEPA and WHO respectively. Using Prati method of classification of surface water quality, the Onyi River fell in the class of slightly polluted water. Weight arithmetic water quality index of 85.2 and metal pollution index of 3.46 corroborated the classification. Hence, adequate treatment of downstream water prior to its use for beneficial purposes is required.

Public Interest Statement

Waste water from industries contaminates rivers if discharged without adequate treatment. Consequently, upon this, most notable rivers in the world whose water resources are to be of benefit to human have been impaired. This study, therefore, focused on the assessment of the degree of contamination of Onyi River in Obajana with waste water from cement production plant. Upon the receipt of such water, the quality of the river was found unfit for beneficial purpose.

1. Introduction

Rivers are the major source of surface water for drinking, domestic, irrigation and industrial purposes which are of tremendous benefits to humans. Monitoring of water quality of rivers regularly is quite necessary for the assessment of water quality for beneficial purposes. One of the several approaches that can be used to assess the water quality status of rivers is to adopt water quality index (WQI) method (Goher, Hassan, Abdel-Moniem, Fahmy, & El-sayed, 2014). WQI is a mathematical expression utilised to transform large number of water quality data into a single number, which denotes the water characteristic (Sutadian, Muttil, Yilmaz, & Perera, 2017). The WQI was first developed in United State by incorporating few commonly used water quality variables, which include dissolved oxygen (DO). pH, conductance, alkalinity and chloride. Since then, several authors have formulated different methods to calculate water quality indices (WQIs). Such WQIs include US national sanitation foundation WQI (Brown, McCleihand, Deiniger, & O’Conor, 1972), Canadian council of ministers of the environment WQI (Khan, Paterson, & Khan, 2003) and Oregon WQI (Kannel, Lee, Lee, Kanel, & Khan, 2007). Upon the application of WQI, the quality of rivers can be categorised as excellent, good, medium, bad and very bad based on the WQI results (Chaturvedi & Bassin, 2010). To obtain data for WQIs, large number of samples are required in water quality measurement with long periods of continuous measurement. This requirement set a limitation to the use of these traditional WQIs. Three-dimensional (3D) fluorescence spectrum index method for river water has been developed to circumvent the difficulties in achieving substantial water-quality data for the use of traditional WQIs. The 3D fluorescence spectrum index has been applied to estimate surface water quality of the Ebinur lake watershed in China (Wang et al., 2017).

The availability of fresh surface water for these purposes is becoming hampered nowadays in the world partly due to municipal and industrial pollution. The vulnerability of rivers to especially industrial pollution is unprecedentedly high because of its unhindered accessibility for disposal of wastes. Pollution from industries constitutes a considerable part of total pollution in the world (Bai, Zhang, Sun, Wang, & Zhu, 2006; Pandey et al., 2005). With the development of industries across the world, rivers have become dumping reservoirs for solid wastes and effluents from industries. A navigable Shitalakkhya River in Bangladesh frequently receives waste from textile and dyeing industries located at Narayangany industrial zone. The waste was known to contain untreated dye with heavy metals (Islam, Sarkar, Rahman, & Ahmed, 2015). The major agro-industrial effluents of sugarcane and starch industries were discharged to the River Nile around Cairo city. Their disposal increased the microbial load of the River (Ali, Sabae, Fayez, Monib, & Hegazi, 2011; El-Sayed & Salem, 2015). The industrial effluent disposal into rivers which resulted to pollution was evident for Lake Calumet in Chicago (Roadcap, Kelly, & Bethke, 2005) and Gorka lake in Poland (Czop, Motyka, Sracek, & Szuwarzyński, 2011). Cement kiln dust was generated as by product from a cement plant in India (Kunal, Rajor, & Siddique, 2016). Like all over the world, Obajana community in Nigeria is encountering tremendous challenge of getting fresh water from the Onyi River. The river plays an important role in the supply of fresh water for bathing, household work and irrigation for Obajana community whose population is about 3,500 (Adejoh, 2016). The river is vulnerable to industrial pollution from a cement plant located in the community. Industrial effluent from the plant essentially contains stream of wastewater, solids and gaseous waste. The plant, however, claimed to have effluent treatment plant whose efficiency is uncertain.

The estimated amount of cement produced globally was 3.6 billion tonnes in which the proportion for Africa was 4.7% (Imbabi, Carrigan, & McKenna, 2012). production of cement in the world is increasing constantly and Nigeria is not exempted. Nigeria, being a developing country is experiencing a high demand for infrastructure and housing which places high demand for cement production (Makinde, 2014; Nyaruai, Kinyua, & Gathu, 2016). The cement production sector in Nigeria is playing a vital role in the Nigeria economic development due to its wide spectrum of usage. The by-products in form of effluent and gaseous waste from the cement plant are also increasing as production is stepped up. The dumping station of the effluent from the cement plant at Obajana is Onyi River. Using the Onyi riverwater for bathing and domestic purposes, the Obajana residents and people who are living at farther distance downstream are prone to skin irritation and cholera.

The assessments of effluent quality from the plant and of water quality of the Onyi River are very much necessary for safe and sound health of the community and river system. The assessment becomes an important tool to understand the effluent impact of the Onyi River. The classification of water quality of the river equally becomes possible with the assessment. Therefore, the objectives of this study were to investigate the quality of effluent from a cement plant, its impact on the Onyi River and to assess the water quality of the river for beneficial purpose. The impact was ascertained by comparison of the effluent quality with the national regulatory standard, National Environment Standards and Regulations Enforcement Agency (2011), for effluent discharges into surface water meant for beneficial purposes such as irrigation, fisheries and swimming and recreation. The consideration of the downstream surface water as fit for drinking and domestic purposes was done by comparison of the water quality with the WHO standard for drinking water. Water-quality indices were also employed to classify the river based on the level of contamination from the effluent discharges. The information about the monitoring of quality of Onyi River in scope and duration is scarce in this regard. Hence, this attempt of frequent monthly monitoring of Onyi River was of environmental essential and could be useful for relevant evaluation of the cement industry. The monitoring covered both wet and dry seasons to study seasonal variations in the water characteristics of the river.

2. Description of study area and sampling design

Obajana Cement plant is the largest cement factory in West Africa and is located in Obajana community on latitude 7.916°N and longitude 6.433°E of Kogi state, The plant is about 60 m away to the Onyi River which frequently receives discharges of effluent directly from the plant. Selected portion of the river with sampling points along the river is shown in Figure 1. Some vegetation grows around the company and the banks of the river. The riverbank is characterised with steep-sided valley. The Fulani settlements are remotely located in the community and access is only via footpaths. The Fulani are nomadic by nature and can settle where there is favourable condition even for their cattle. Occupations of the people in this community include cattle rearing, farming, hunting and petty trading. The crops grown in this area include rice, sweet potatoes, maize, millets, sugarcane, cassava and cowpea.

Figure 1. Selected area of Onyi River at Obajana showing sampling points.

A portion of the Onyi River under investigation was divided into four zones taking reference from the point of discharge of effluent into the river. These zones are the (1) Dam (2) upstream (3) discharge point at which industrial discharge entered the water course and (4) downstream. All the sampling points along the watercourse before the discharge point were referred to as upstream and it serves as the control points, while all those sampling points after the discharge point were referred to as downstream. The sampling points are designated as follows:

3. Sampling and chemical analysis of samples

Effluents and water samples of 2.5 L each were collected using grab sampling technique at the designated sampling point monthly for a year. They were kept at 4°C in ice chests and transported to the laboratory. In the laboratory, analyses were carried out immediately. A total of 36 effluent samples and 132 water samples were collected into polyethylene containers soaked in 2 M HNO₃, washed and rinsed with distilled water prior to sampling. All analyses were carried out using standard procedures of the American Public Health Association, American Water Works Association & Water Environmental Federation (1998). The physicochemical qualities of the samples were determined. The pH of samples was determined by electrometric method using a pH meter (HANNA, model HI 96107). Total alkalinity, total hardness, calcium and magnesium were determined by titrimetry. Gravimetry method was used for total solid (TS), total suspended solids (TSS) and total dissolved solids (TDS). Turbidity was determined by turbidimetry method. This method is based on the comparison of the intensity of UV/Visible light scattered by the sample solution with that of 400 FTU. The absorbance values of the solutions were determined using NICOLET Evolution 300 UV/Visible spectrophotometer. Sulphate, nitrate and phosphate were determined by colorimetry. Colorimetric determination of sulphate was performed with barium chloride solution as reagent. Colorimetric phenoldisulphonic acid method was used for nitrate while molybdenum blue method was employed for phosphate. In each of these methods, the absorbance values of the colour solutions were measured with spectrophotometer.

Alkaline-azide modification of Winkler’s method was used for dissolved oxygen and biological oxygen demand (BOD). Open reflux method involving the oxidation of organic matter of sample in acidic medium and titration with ferrous ammonium sulphate was used for chemical oxygen demand (COD). Heavy metals (Cd, Co, Cr, Cu, Ni, Pb and Zn) were determined by atomic absorption spectrophotometry using Buck 205 Atomic Spectrophotometer after the digestion of samples with concentrated nitric acid.

All the reagents were of analar grade. Sample blanks were collected for the determinations of anions and metals and appropriate corrections were made. The recovery study of heavy metals in samples was carried out and percentage recoveries of 90.1–110% (Co), 89.4–102% (Cd), 94.3–106% (Cr), 86.7–90.0% (Cu), 90.0–103% (Ni), 98.6–101% (Pb) and 92.5–105% (Zn) were obtained.

4. Application of water quality and pollution indeces

The suitability of water from the river downstream was investigated using weighted arithmetic WQI and metal pollution index (PI) as described by Brown et al. (1972) and Caeiro et al. (2005) respectively. The downstream physicochemical parameter values together with WHO standard permissible limits of the parameter were employed to evaluate the mathematical.