IMPACT OF FRESH AND FERMENTED PALM OIL MILL EFFLUENTS ON SOIL PHYSICOCHEMICAL PARAMETERS AND ENZYME ACTIVITIES IN UMUAKA NJABA IMO STATE OF NIGERIA

ABSTRACT

The impact of palm oil mill effluents (POME) on soil fertility was determined by studying the physico-chemical and heavy metals parameters found in fresh and fermented POME from six palm oil milling sites. Some soil enzymes (like catalase, dehydrogenase and lipase) and physico-chemical parameters of POME polluted soil wereevaluated from six dumpsites and soil from ten-yards distance from dumpsites in relation to the control farmland in the area. The fresh and fermented  POME samples were randomly  collected aseptically from small scale palm oil milling sites in Umuaka inNjaba Local Government Area ofImo State, Nigeria. The soil samples were collected  aseptically into  sterile containers from topsoil (0 – 15cm deep), and subsoil (15 – 30cm deep) at dumpsites, ten-yards distance from dumpsites and farmland one kilometre from various dumpsites. The study of both soil and POME samples were carried out using standard analytical procedures. The analysis of variance of the results of physicochemical parameters in POME samples showed that there were significant(p<0.05) differences in all the parameters which include: pH, magnesium ion (Mg2+), calcium (Ca2+), potassium (K+), sodium (Na+), total solid (TS), suspended solids (SS), total volatile solids(TVS),  chemical  oxygen  demand  (COD),  dissolved   oxygen  (DO),  nitrogen  (N)   and phosphorus  (P)   in fermentedPOME  when compared  tofresh POME.The  concentration  of heavy metals in the POME samples showed that they were rich in chromium, copper, iron and lacked cadmium. The results of the soil fertility parameters showed that POME polluted soils are rich in soil nutrients such as nitrogen, organic carbon (OC), organic matter (OM), cation exchange capacity (CEC)  and most especially exchangeable cations (Mg2+, Ca2+, K+ and Na+) in topsoils and subsoils than in their respective non POME polluted soils. Although the results of the soil fertility  analysis showed that POME-polluted  soil had high fertility index, it has low phosphorus content which was due to negative effect of the acidic pH of the POME on phosphorus availability.The analysis of the results of  activities of soil enzymes in the  POME- polluted soil showed that discharge of the fresh and fermented POME caused induction of lipase activity. Catalase activitydecreasedsignificantly  (p<0.05)from 1.35±0.02to 0.33±0.01 mM H2O2/g soil/h for topsoil and 2.08±0.08 to 0.21±0.01mM H2O2/g dry soil/h for subsoil from dumpsites respectively while dehydrogenase activity in topsoil and subsoil ten  yards away from dumpsitedecreasedsignificantly  (p<0.05)from  1.35±0.02  to  0.18mM H2O2/g soil/h and  2.08±0.08 to 0.21±0.01mM H2O2/g dry soil/h,respectively. Dehydrogenase activitydecreasedsignificantly  (p<0.05) from 0.76±0.001 to 0.10 mg/gdrysoil/96h for topsoil and 0.86±0.01  to 0.077±0.01mg  formazan/gdrysoil/96h  for subsoil  from dumpsites  while dehydrogenase      activity      in     topsoil      and      subsoil      ten     yards     away     from dumpsitedecreasedsignificantly        (p<0.05)        from        0.76±0.001        to        0.10±0.03 mgformazan/gdrysoil/96h     and     0.86±0.01     to     0.07±0.01     mgformazan/gdrysoil/96h, respectively. Furthermore, the results obtained for the soil pH indicate that the soils are acidic and have high exchangeable acidity.  Considering the high fertility potentials of POME, it is necessary to make good effort to maximize these potentials by reducing its high pollution level such as BOD, COD, heavy metals, oil and grease in the fresh and fermented POME.

CHAPTER ONE

INTRODUCTION

Palm oil mill effluent (POME) has been a major environmental concern in countries producing  them. This effluent  is a land and aquatic pollutant  when  discharged  fresh and fermented due to the presence of moderate amount of organic  load  in it and its phytotoxic properties (Okwute and Isu, 2007). The uses of wastes such as POME in agriculture and for land reclamation are a common practice in regions with its abundant supply especially for irrigation,  soil  conditioning,  amendment  and  conservation  purposes  (Navas  et al.,  1998; Pascual et al., 2007). Palm oil production requires addition of large quantity of water which is eventually discharged as waste effluent (Nwoko and Ogunyemi, 2010). POME is a mixture of water,  oil and  natural  sediments  (solid  particles  and  fibres),  large  quantity  of  which  is generated annually during crude palm oil production (Salihu et al., 2011b) and is amenable to microbial degradation (Nwoko and Ogunyemi, 2010; Nwoko et al., 2010).  POME includes dissolved  constituents  such  as  high  concentration  of  protein,  carbohydrate,  nitrogenous compounds,  lipids  and  minerals,  which  may  be  converted  into  useful  materials  using microbial processes. Nevertheless, POME if not discharged properly and treated, may lead to considerable  environmental  problems  (Singh  et  al.,  2010).  In  nature,  both  nitrogen  and phosphorus come from the soil and decaying plants and animals (Logan et al., 1997; Navas et al., 1998).  Fertilizers,  fresh and fermented  sewage  as well as domestic  and wild  animal wastes are common sources of plant nutrients.

The input of effluent materials with high organic matter content will help replenish the soil for sustainable agriculture. POME application to soil can result in increases of some beneficial  soil chemical  and  physical  characteristics  such as  increases  in organic  matter, carbon,  major  nutrients  (such  as  nitrogen,  potassium,  calcium,  and  magnesium),  water- holding capacity and porosity (Logan et al., 1997; Navas et al., 1998). However, it may bring about undesirable changes such as decrease in pH and increases in salinity (Kathiravale and Ripin, 2000). These effects mostly occur very slowly and take many years to be significant. Soil  microbiological  and  biochemical  properties  have  been  considered  early as  sensitive indicators of soil changes and can be used to predict long – term trends in the quality of soil (Ros et al., 2003). Soil microbial properties are equally affected by environmental factors. (Dick  and  Tabatabai,  1992)  reported  that  high  rate  of  inorganic  fertilizer  application suppresses microbial respiration and dehydrogenase activity. Other factors such as increase in salinity or decrease in water availability may also reduce biological activity (Paredes et al.,

2005). POME contains high organic load, substantial amounts of plant nutrients and represent a low cost source of plant nutrients when fermented  (Onyia et al., 2001). It  is generally believed that the toxic effect of POME is due to its possession of phenols and other organic acids which are responsible for phytotoxicity and antibacterial activity (Capasso et al., 1992; Piotrowska  et al., 2006).  However,  the polyphenolic  fraction  is  degraded  with time  and partially transforms into humic substances (Piotrowska et al., 2006).   Little information is known on the impact of POME on the biochemical and microbial properties of soil. Studies show that effects of wastes applied to soil occurred mainly in the first weeks after amendment (Martens et al., 1992; Perucci, 1992; Binder  et al., 2002). Indeed, investigating the effects POME  has on soil properties  would  help farmers  mostly in rural areas to improve  food production through expanding their understanding of the importance of POME as well as the quantity to be added to soil during farming operation prior to planting. Also, knowledge on the remediating effect  of POME on the soil will assist government in its drive to increase food production by helping farmers to improve soil fertility through adequate harnessing and processing of POME (Nwoko and Ogunyemi, 2010).

1.1 Scientific Classification of Oil Palm (Elaeis guineensis)

Elaeis  guineensis  is a member  of the  family Arecaceae  (Reeves  and  Weihrauch,

1979). It is native to West and Southwest Africa and is vastly cultivated as a source of oil in Nigeria. It has a lifespan of over 200 years, while the economic life is about 20-25 years. The nursery period is 11-15 months and first harvest is done 32-38 months after planting (Reeves and  Weihrauch,  1979).  The  yield  is  about  45-56%  of  fresh  fruit  bunch  and  the  fleshy mesocarp of the fruit is used as oil source. The yield of oil from the kernel is about 40-50% (Rupani et al., 2010). The plant is classified as follows:

Kingdom                    Plantae Division                      Magnoliophyta Class                           Liliopsida Order                          Arecales Family                        Arecaceae Genus                         Elaeis

Specie                         Elaeis guineensis.

Source: Reeves and Weihrauch (1979).

While  oil palm  is  recognized  for  its  contribution  to  economic  growth,  the  rapid development of palm products has also correspondingly led to environmental pollution.

1.2 The Palm Seeds

Palm seeds are reddish, about the size of a large plum and grow in large  bunches. Each fruit is made up of an oily and fleshy outer layer (the pericarp) with a single seed (the palm kernel) that is also rich in oil. The seeds are used for propagating the plant and are eaten roasted or boiled. The pulp is pressed to produce palm oil while the kernel is used to produce palm kernel oil (Rupani et al., 2010).

Fig 1: Fresh fruit bunch (FFB).                                          Fig 2: Palm seeds

One of the seeds was cracked open to show the pulp segment, the kernel shell and the kernel seed.

1.3 The Palm Oil Production

Palm oil is edible oil derived from the fleshy mesocarp of the fruit of oil palm. It is one of the most widely consumed plant oil across the world (Rupani et al., 2010). In general, the palm oil milling process can be categorised into dry and wet (standard) processes. The wet process of palm oil milling is the most common and typical way of  extracting palms especially in Nigeria (Okwute and Isu, 2007). Despite the fact  that  the POME can cause environmental  pollution, not much has been done to  mitigate  this effect. The technology applied in almost all palm oil mills is based on  methods developed in the 1970s and 80s (Zaini et al., 2010). The major  steps in the  oil palm processing  as reported  by Zaini et al.(2010) are as follows:

Threshing:  This  is the  removal  of  fruits  from  bunches.  The  fresh  fruit  bunches consists of the fruits that are attached onto the spikelet growing on a main stem. The fruit- laden spikelet are cut from the bunch stem using axe for manual threshing before separating the fruits from the spikelets (Zaini et al., 2010).

Sterilisation:  Loose  fruits  are  boiled  in batches  using  high temperature  wet-heat treatment. This is carried out in autoclave by steam application at temperature and pressure ranges of 120-140°C at 3-3.5 bar, for 75 minutes. Boiling prevents fatty acid formation and assists in fruit stripping as well as prepares the fruit fibre for the next processing step. Boiling breaks down oil-splitting enzyme and stops hydrolysis and auto-oxidation(Zaini et al., 2010).

Crushing  process:  In this  step  the  palm  fruits  are  passed  through  shredder  and pressing machine to separate the oil from the fibre and seeds (Zaini et al., 2010).

Digestion of the Fruit: This process releases the palm oil in the fruit through cracks in the oil-bearing cells. The digester consists of a steam-heated cylindrical vessel with central rotating shaft that is filled with several beater arms. The fruit is pounded by the rotary beater arms at high temperature to reduce the oil viscosity. This destroys the exocarp fruits or the outer covering and completes the disruption of the oil cell already begun in the sterilisation process. The digester must be filled to ensure the maximum  storage and the effect of the agitation (Zaini et al., 2010).

Extracting the Palm Oil: There are two distinct methods of extracting oil from the digested palm fruit: one system uses mechanical presses and is called the “dry” method. The other called the “wet” method uses hot water to leach out the oil (Zaini et al., 2010).

Kernel Recovery – The residue from the press consists of a mixture of fibres  and palm nuts which are at this stage sorted. The sorted fibres are covered and  allowed  to be heated by itsinternal exothermic reactions for about two or three days.  The fibres are then pressed in spindle press to recover second grade (technical) oil that is used normally in soap making. The nuts are usually dried and sold to other operators who process them into palm kernel oil (Zaini et al., 2010).

Refining: Refining converts the crude palm oil (CPO) into refined form. The CPO is processed to segregate fat and obtain refined palm oil (Zaini et al., 2010).

Oil Storage: The palm oil is stored in large steel tanks at 31 to 40°C to keep it in liquid form during bulk transport. The tank headspace is often flushed with CO2  to prevent oxidation. Higher temperatures are used during filling and draining of the tanks (Zaini et al., 2010).

Fig 3:Palm oil mill effluent dumpsite

KEY:

a = Fermented POME

b = Fresh POME

Table 1: Summary of Unit Operations in Palm Oil Production (Rupani et al., 2010)

1.4 The Properties of POME

The two main wastes resulting from palm oil production in oil mills are the solid and liquid wastes (Kathiravale and Ripin, 1997). The solid waste typically consists of palm kernel shells (PKS), mesocarp fruit fibres (MFF) and empty fruit bunches (EFB). The liquid waste generated from the extraction of palm oil in wet process comes mainly from the oil room after the kernel recovery.  This liquid waste combined  with  the wastes  from the steriliser condensate and cooling water is called palm oil mill effluent (POME) (Zaini et al., 2010).

Palm  oil production  requires  input of large quantity of water  which is  eventually discharged as waste effluent. POME is an effluent generated from palm oil milling activities which   requires   effective   treatment   before   discharge   into   watercourses   (Nwoko   and Ogunyemi,    2010).    POME    generated    from    mill    operation    is    thick,    brownish, highlyconcentrated,colloidal and slurry with pH ranging from 4.0 to 4.5 and a temperature of between 80 and 90°C (Zaini et al., 2010; Alrawi et al., 2012). It contains mainly water (95-

96%), suspended solids (2-4%) and oil and grease (0.6-0.7%) (Ahmad et al., 2003). Palm oil production process does not utilize any chemical and hence POME is considered as a non- toxic wastewater.

Table 2: Characteristics of POME and its respective standard discharge limit

Parameters                              Experimental  values  obtained  by  some  previous

researchers on POME.

Standard

limit (mg/L)

pH	4.7	3.8-4.4	4.24-4.66	5-9
Oil and grease (mg/L)	4,000	4,900-5,700	8,845-10,052	50
Biological  oxygen demand   (mg/L)   Chemical oxygen	25000       50,000	23,000-26,000       42,500-55,700	62,500-69,215       95,465-112,023	100       –
demand (mg/L)   Total solids (mg/L)	40,500	–	68,854-75,327	–
Suspended solids (mg/L) Total nitrogen (mg/L)	18,000       750	16,500-19,500       500-700	44,680-47,140       1,305-1,493	400       150
Total       volatile       solids	34,000	–	4,045-4,335	–
(mg/L)

Sources: Department of EnvironmentMalaysian, (1999); Ahmad et al., 2003; Najafpou et al.,

2006; Choorit and Wisarnwan(2007).

1.4.1    Physicochemical Characterisation of POME

1.4.1.1 Dissolved Oxygen (DO)

The dissolved oxygen is a measure of the amount of gaseous oxygen dissolved in an aqueous solution. Analysis of DO is a key test in water pollution. The DO levels in POME depend  on the  physical,  chemical  and biochemical  activities  in POME.  Adequate  DO is necessary for good quality of water. Oxygen is an essential element to all forms of life. The DO concentrations ought not to exceed 110% otherwise; it may be harmful to aquatic life. As DO levels  in water  drop below 5.0 mg/L,  aquatic  life  is  put under  stress;  the lower  the concentration of DO, the greater the stress. Death usually occurs at concentrations less than 2 mg/L. The World Health Organization (WHO)  suggested the standard of DO greater than

5mg/L for river water monitoring (Sehar et al., 2011).

1.4.1.2 Biochemical Oxygen Demand (BOD)

The standard, five-day BOD (BOD)  value is commonly used to determine the amount of organic pollution in water and wastewater. Determination of BOD involves measuring the oxygen demand of both the organic matter and organism in the POME. BOD is the amount of dissolved oxygen needed by aerobic biological organisms in a body of water to break down organic material present in a given water sample at certain temperature over a specific period of time (Okwute and Isu, 2007). It is an empirical test that determines the relative oxygen requirements of wastewater, effluents and polluted water. BOD tests measure the molecular oxygen utilised during a specified  duration incubation for the biochemical  degradation  of organic materials (carbonaceous demand) and the oxygen used to oxidise inorganic material such as ferrous iron and sulfides (Sehar et al., 2011).

1.4.1.3 Chemical Oxygen demand (COD)

The chemical oxygen demand (COD) is used to measure the oxygen equivalent of the organic  material  in  wastewater.  It  is  a  useful  measure  of  water  quality.  In  most  cases applications of COD determine the amount of organic pollutants found in water (Sehar et al.,

2011).  The  COD  test  is  commonly  used  to  indirectly  measure  the  amount  of  organic compounds  in water.  The COD  is the amount  of oxygen required  to  chemically oxidize organic  water  contaminants  to  inorganic  end  products  (Okwute  and  Isu,  2007).  Most applications of COD determine the amount of organic pollutants found in surface water. COD is often measured as a rapid indicator of organic pollution in water (Sehar et al., 2011).

1.4.1.4 Total Dissolved Solids (TS)

The  total  solids  represent  all  solids  in  a  water  sample.  They  include  the  total suspended solids, total dissolved solids, and volatile suspended solids. The range of 37900 –

45 000 mg/L has been reported by Wood et al. (1979); Wong et al. (2009) and  MPOB (2004). TS is a measure of the amount of filterable solids in a water sample (Sehar et al.,

2011).

1.4.1.5 Total Suspended Solids (SS)

These are amounts of filterable solids in a water sample. POME samples are filtered through a glass fibre filter. The filters are dried and weighed to determine the amount of total suspended solids in mg/L of sample. Suspended solid of POME were reported to be 18,000 mg/L by Ahmad et al. (2003) and MPOB (2004). The higher  suspended solid was 25,800 mg/L and was recorded by Wu et al., 2007

1.4.1.6 Volatile Suspended Solid (TVS)

Volatile solids are those solids lost on ignition (heating at 550 0C). They are useful in application  for treatment  plant operator  because  they give a rough approximation  of  the amount of organic matter present in the solid fraction of wastewater, activated  sludge and industrial wastes. Wood et al. (1979) and Wong et al. (2009) reported VSS range of 27300 mg/L to 30150 mg/L.

1.4.1.7 Oil and Grease (O and G)

Oil and grease have poor solubility in water. Thus, oil and grease content of industrial wastes are important  consideration  in handling and treatment  of the material  for disposal (Salihu et al., 2011a). The concentration of oil in effluents from different industrial sources can be as high as 40,000mg/L  (Arcadio  and Gregoria,  2003).  Unlike free or floating oil spilled  in the sea, lakes or rivers, most of the industrial  wastewaters  contain oil-in-water emulsions among other basic contaminants. Emulsified oil in wastewater can lead to severe problems in different treatment stages. Oil in wastewaters has to be removed in order to: (1) prevent interfaces in water treatment units (2) reduce fouling in process equipment (3) avoid problems in biological treatment  stages and (4) comply with water discharge requirements (Arcadio and Gregoria, 2003).

1.5 Heavy Metals

The term heavy metal refers to any metallic chemical element that has a  relatively high  density  and  is  toxic  or  poisonous  at  low  concentrations  (Kızılkaya  et  al.,  2004). Examples of heavy metals include mercury (Hg), cadmium (Cd),  arsenic  (As), chromium (Cr), thallium (Tl), and lead (Pb) (Lebedeva et al., 1995). The use of metals by humans was and is still accompanied by increasing inputs of metals into soils through different types of wastes (Welp, 1999). The major sources of chromium include the metal finishing industry, petroleum  refining,  leather  tanning,   iron  and  steel  industries,  production  of  inorganic chemicals,  textile manufacturing  and pulp production.  Because metals persist in soils and their leaching is a very slow process, they tend to accumulate in the soils (Irha et al., 2003). Chromium is one of the heavy metals and has oxidation states ranging from chromium (III) to chromium (VI).Chromium compounds are stable in the trivalent state and occur in nature in this  state  in ores such as ferrochromite,  while  chromium  (VI) is usually  produced  from anthropogenic sources (Cervantes et al., 2001). Hexavalent chromium compounds have been used in a wide variety of commercial processes (Turick et al., 1996). Upon the reduction of

chromium (VI) to chromium (III), the toxic effects are significantly decreased in  humans, animals and plants because of a decrease in the solubility and bioavailability of chromium (III) (Turick et al., 1996). The reduction of the highly toxic and mobile Cr (VI) to the less toxic and less mobile Cr (III) is likely to be useful in the remediation of contaminated waters and  soils.  This  problem  has  stimulated  interest  in   microorganisms   as  alternatives  to conventional  methods  due to their eco-friendly  nature.  Cr (III) is transformed  to Cr (VI) mainly inside root cells but also in the aerial  part of plant (Cervantes et al., 2001). Roots accumulate 10-100 times more Cr than shoots and other tissues. As a consequence, inhibition of  growth,  photosynthesis  and  respiration  processes  in  plants  and  microorganisms  are observed (Cervantes et al., 2001). Reduction of soluble Cr (VI) to insoluble Cr (III) occurs only within the surface layer of aggregates with higher available organic carbon and higher microbial   respiration  (Tokunaga  et  al.,  2003).  Thus,  spatially  resolved  chemical  and microbiological measurements are necessary within anaerobic soil aggregates to characterise and predict the fate of chromium contamination (Tokunaga et al., 2003). Heavy metals can enter a water supply by industrial and consumer waste or even from  acidic rain, breaking down soils and releasing heavy metals into streams, lakes, rivers and groundwater (Zheng et al., 1999). The impacts of elevated heavy metal levels on the size and activity of natural soil microbial communities  have been well documented.  Field studies of metal -contaminated soils have shown that elevated metal loadings can result in decreased microbial community size (Jordan and LeChevalier,  1975; Brookes  and McGrath,  1984; Chander  and Brookes,

1991; Konopka et al., 1999) in organic matter mineralisation (Chander and Brookes, 1991)

and leaf litter decomposition (Strojan, 1978).

1.5.1 Impact of Heavy Metals on the Soil Enzymes

By taking part and playing an important role in chemical changes of carbon, nitrogen, phosphorus and sulphur compounds,  soil enzymes can serve as a tool for  determining the biochemical  soil  properties  (Dick  and  Tabatabai,  1992).  For  this  purpose,  activity  of dehydrogenases  is most commonly assayed  as it is usually  positively correlated  with the volume of yields which in turn may indirectly indicate,  however, that the activity of those enzymes is related to soil fertility (Dick, 1997). The activity of other soil enzymes such as catalase, lipase, urease or phosphatase, can also be helpful because they are as sensitive as dehydrogenases   in  indicating  processes   occurring  in  soil.  Soil  enzyme  activities  are considered  to  be  sensitive  to  pollution  and  have  been  proposed  as  indicators  of  soil degradation  (Trasar-Cepedaet  al., 2007). Catalase  (hydrogen peroxide oxidoreductase,  EC1.11.1.6)  is  an  intracellular  enzyme  found  in  all  aerobic  bacteria  and  most  facultative anaerobes  but  absent  in  obligate  anaerobes  (Trasar-Cepedaet  al.,  2007  and  Shiyinet  al., 2004).

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