ABSTRACT
This study is aimed at the assessment of sawdust activated carbon in the treatment of aquaculture effluent with various objectives which includes the determination of the SAC properties, effluent parameters, effect of operating conditions and application of relevant adsorption isotherms. The sawdust was first precarbonized at 500 C, then impregnated with potassium carbonate (activating agent) and activated at 450 C in a furnace. The surface morphology of the sawdust activated carbon (SAC) was determined using scanning electron microscope (SEM) which showed a very porous media. It was further characterized using BET surface area at 77K, and the resulting surface area was 831.83 2/g. The acquaculture effluent (AE) was found to be very polluted compared to the NESREA discharge standard, in COD, TSS, BOD,NITRATES and lead(II) ion. An optimization studies was done using batch treatment process at varying dosage, time and initial concentrations, and the optimum treatment dosage and time were found to be 2g/l at 60minutes which gave an overall 83.33% reduction of COD, 90.80% reduction of BOD, 73.24% removal of nitrate( 3), 93.23% removal 0f TSS, and 99.35% removal of lead (Pb) ions. According to the 2 values, the kinetic studies showed that the adsorption process was a pseudo second order reaction with a 2 value of 0.99. After the assessment, it was found that among other uses of sawdust, it is also a good precursor for the production of activated carbon, which is has been found in this study to be a good treatment media for the treatment of the polluted aquaculture effluent prior to its disposal into the environment.
CHAPTER ONE
INTRODUCTION
1.1 General Background
Aquaculture can be described as the production of aquatic organisms, both plant and animal under controlled or semi-controlled conditions (Summerfelt, 2003). However, Adewumi(2015), defined aquaculture practice in Nigeria as the rearing of fish in an enclosed and fairly shallow body of water where all its life processes is being controlled.
According to Sanjaya (2013), untreated aquaculture effluent generally contains high levels of organic material, numerous pathogenic micro-organisms, as well as nutrient and its indiscriminate discharge may lead to serious environmental and health hazards if not treated appropriately before final disposal. Therefore, as the population increases and aquaculture practice expands, it is important to provide for an adequate waste management strategy to ensure a favourable environmental condition.
Typical wastewater from an aquaculture facility may include feaces and nutrients from excretion by aquatic animals, as well as uneaten feeds and chemicals such as drugs and cleanser residues (Boyd, 2003). Aquacultural effluents contains dissolved and suspended solids that are basically oxygen demanding materials which makes the effluent to be high in biochemical oxygen demand(BOD) and nutrients like phosphorus (P) and nitrogen (N) which stems from fish excretion, feaces, and uneaten feed (Boyd, 2000). Overtime, significant discharge of this untreated effluent into lakes, rivers, estuaries or any other receiving waters could cause adverse environmental impacts such as eutrophication.
Although , there is a suggestions on the re-use of aquaculture effluent (Yeo et al., 2004), which includes its use in irrigation of crops, but this has been found to be impractical in urban areas where aquaculture is striving but crop farming is done on a very small scale. Therefore, since discharge of aquaculture effluent is inevitable, several environmental protection agencies and Global Aquaculture Alliance (GAA) which advocates, educates and demonstrates responsible aquaculture practices for the industry, have recommended waste water treatment and also set an effluent discharge limit (Boyd and Gautier, 2000).
In many instances however, secondary wastewater treatment such as trickling filters, oxidation ponds and aerated lagoons has been found inadequate in the treatment of certain waste water, hence the need to apply appropriate tertiary/advanced wastewater treatment methods, among which is adsorption. Common advanced wastewater treatment methods are ion exchange, membrane separation, electrolysis and adsorption. Among these methods, adsorption technology has gained a wider application due to its inherent low cost, versatility and robustness (Dimple, 2014). The other related technology are quite expensive, requiring a high level of technical know-how, steady energy supply, and chemicals along with specific equipments which may not be readily available, especially in developing countries.
Activated carbons are produced from a solid carbonaceous based material, which is non-graphitic, which has an initial isotropic structure (Diaz and Martin, 2006). The raw material is activated by means of medium to high temperature treatments, which removes solid mass, and at the same time, create pores where the removed mass was previously
located (Marshahida et al, 2016). The common properties of activated carbons and other kinds of carbon adsorbents is their well-developed pore network (McDougall, 1991).
Since an activated carbon is structurally a non-graphitic carbonaceous material, almost any carbonaceous solid material can be converted into activated carbon. There are therefore plenty of possible raw materials such as wood, lignocellulosic biomass, peat, lignite and coals that can be used to make activated carbon. In practice, wood, coconut shells, fruit stones, coals, lignites and petroleum coke, are all inexpensive materials with high carbon content and low inorganic content, and consequently, these are suitable precursors for use as an activated carbon (Diaz and Martin, 2006).
Saw dust is a waste material from the timber industry, produced when timber is sawn into planks at saw mills. This process is a daily activity causing heaps of saw dust to be generated after each day. The need to convert this waste product into a useful by-product is the focus of the study. The size of sawdust particles depends on the kinds of wood from which the sawdust is obtained and also on the size of the saw teeth (Afuwape, 1983). About 10-13% of the total volume of the wood log is reduced to sawdust in milling operations and this sawdust generally depends largely on the average width of the saw kern and the thickness of the timber sawed (Paulrud et al., 2002). Sawdust has been used for several purposes, including sawdust briquettes, partial replacement of concrete, soil stabilization and also as an adsorbent.
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