BIOREMEDIATION OF SUGAR INDUSTRY EFFLUENT

Rachel H. Cawit, ChE, MScI. INTRODUCTION

The sugar industry is one of the most important agro-based industries, which plays an important role in economic development in the Philippines. However, just as any industries have drawbacks, the effluents released by sugar industry produce a high degree of organic pollution in both aquatic and terrestrial ecosystem that can alter the physico-chemical characteristics of the receiving water body, affecting aquatic flora and fauna. Hence, it is but imperative to find for an efficient treatment program for sugar industry effluent that can comply with environmental regulations and render its discharge or re-use harmless to the ecosystem.

Out of several methods that are used in the treatment of industrial effluents, biotreatment offers a cheaper and environmentally friendly alternative for biological degradation of industrial effluentsBioremediation is a pollution control technology that uses biological systems to catalyze the biodegradation or transformation of various toxic chemicals to less harmful forms. This natural process bioremediation includes bioengineering, the capabilities of intrinsic microorganisms to clean the environment is an effective alternative to conventional remediation methods. It uses microorganisms, plants or their enzymes to return to the natural environment materials altered by contaminants to its original condition. Bioremediation can occur on its own (natural attenuation or intrinsic bioremediation) or can be spurred on via the addition of fertilizers to increase the bioavailability within the medium (biostimulation). Recent advancements proved successful in the addition of matched microbe strains to the medium to enhance the resident microbe populations ability to break down contaminants.

Bioremediation is an option that offers the possibility to destroy or render harmless various contaminants using natural biological activity. It uses simple, relatively low cost, aesthetically pleasant technology that have high public acceptance.

Although the methodologies employed in bioremediation are not technically complex, considerable experience may be required to design and implement optimum operational conditions to achieve satisfactory result. The efficiency of operating biological processes is necessarily dictated by how well one understands the effects of process conditions to the microorganisms.

II. PRINCIPLES OF BIOREMEDIATION

In bioremediation, the microorganisms break down contaminants by using them as an energy source or cometabolizing them with an energy source. More specifically, it involves the production of energy in a redox reaction within microbial cells. These reactions include respiration and other biological functions needed for cell maintenance and reproduction. A delivery system that provides one or more of the following is generally required:

1. Energy source (electron donor), 2. Electron acceptor, and 3. Nutrients. Different types of microbial electron acceptor classes can be involved in bioremediation, such as oxygen-, nitrate-, manganese-, iron (III)-, sulfate-, or carbon dioxide-reducing , and their corresponding redox potentials. Redox potentials provide an indication of the relative dominance of the electron acceptor classes (EPA 2000). Generally, electron acceptors and nutrients are the two most critical components of any delivery system (EPA 2004).

To stimulate and enhance microbial activity, microorganisms (bioaugmentation) or amendments (biostimulation), such as air, organic substrates or other electron donors/acceptors, nutrients, and other compounds that affect and can limit treatment in their absence can be added. Biostimulation can be used where the bacteria necessary to degrade the contaminants are present but conditions do not favor their growth (e.g., anaerobic bacteria in an aerobic aquifer, aerobic bacteria in an anaerobic aquifer, lack of appropriate nutrients or electron donors/acceptors). Bioaugumentation can be used when the bacteria necessary to degrade the contaminants do not occur naturally at a site or occur at too low of a population to be effective. Biostimulation and bioaugmentation can be used to treat soil and other solids, groundwater, or surface water (EPA 2006).

The first step of any bioremediation program is to develop a conceptual model to evaluate the potential for applying bioremediation. This model takes into account the nature and extent of contamination of the waste being handled, as well as its biodegradation potential and oxidation-reduction conditions. Once wastewater characteristic has been defined, a characterization of the existing microbial community, or the characteristics necessary for the establishment of an appropriate microbial community, can be determined. Activities undertaken prior to the implementation of a bioremediation program often involve treatability studies and the structure and function of the microbial community to ensure that undesirable reactions with the contaminants or their degradation products are prevented. The success of a bioremediation application highly depends on characterization and monitoring completed before and during its implementation (Hazen 2010).

III. TYPES OF BIOREMEDIATION

Aerobic bioremediationinvolves microbial reactions that require oxygen to go forward. The bacteria use a carbon substrate as the electron donor and oxygen as the electron acceptor.

Anaerobic bioremediationinvolves microbial reactions occurring in the absence of oxygen and encompasses many processes, including fermentation, methanogenesis, reductive dechlorination, and sulfate- and nitrate reducing conditions. Depending on the contaminant, a subset of these activities may be cultivated. In anaerobic metabolism, nitrate, sulfate, carbon dioxide, oxidized materials, or organic compounds may replace oxygen as the electron acceptor.

Cometabolic bioremediation involves microbes that do not gain energy or carbon from degrading a contaminant. Instead, the contaminant is degraded via a side reaction. (EPA 2006).

IV. FACTORS AFFECTING BIOREMEDIATION

The control and optimization of bioremediation processes is a complex system of many factors. These factors include:

a. The existence of a microbial population capable of degrading the pollutants:

Living organisms are chemical machines. Microorganisms have evolved a variety of enzyme regulatory mechanisms to accommodate the changing needs of the microbial cell in a changing environment. Microorganisms degrade pollutants through the various enzymes they produce. They involve numerous chemical reactions, each broken down by a specific enzyme. The breaking down of available nutrients and the building of cell constituents are not single step processes.

Enzymes are the microbes catalysts, they speed that process without being used up in the reaction. A living cell contains more than 1000 different enzymes, each an effective catalyst to some chemical reaction. These enzymes must act together and sequentially in a coordinated effort so that all chemical activities in the cell are smoothly integrated with one another. One consequence of this enzyme coordination is the making and distribution of materials as required by the microbe for normal growth and metabolism.

b. The availability of contaminants to the microbial population;

Bioavailability of the substrate is directly related to the available substrate surface area. The more surface area that is exposed to the microbes the more efficiently they can subject the substrate to their secreted enzymes.

When the substrate (pollutant-contaminant) is emulsified into colloidal sized droplets smaller than the microorganisms, it can be more efficiently used thus enhancing and greatly speeding degradation. Whether referring to bioremediation performed by indigenous (on site) or added microorganisms, any acclimatized microbe will use the pollutant more efficiently as food when it is served to them individually.

Bioavailability enhancing mixtures exponentially augment all microbes by making their food more available to the microbes and their multitudes of rapidly produced descendants. This is best accomplished by breaking the substrate into tiny droplets (colloids) which are suspended in water thereby increasing the surface area available to the microbes. Microbes capable of producing enzymes that act on the hydrocarbons must be present with adequate moisture and minerals supplied if necessary. The major consideration then must be the bioavailability of the substrate.

The use of any chemicals detrimental to the microbes will diminish or destroy subsequent microbial activity and bioremediation. Bioavailability enhancing agents should not only more rapidly prepare the food (substrate) for the microbes but at the same time act as a food source for them. By adding the microbes to the enhancing agents prior to use, the microbes can begin to repair their tissues and enzyme systems and thus more rapidly initiate the bioremediation response.

c. Environment factors (temperature, pH, presence of oxygen or other electron acceptors, and nutrients).

Hydrocarbons are suitable sources of carbon (food) for microbial cell growth and energy. The relative complexity of the substrate determines the ease and speed of bioremediation. The more complex molecules require more microbial activity because of the many possible intermediate breakdown products produced.

Oxygen is essential for most organisms yet can be poisonous to others. In aerobic bioremediation oxygen must be present for degradation to occur. The hydrocarbon is broken down yielding water (H20) and carbon dioxide (C02) as end products. Note that oxygen atoms are added to the hydrogen and carbon components of the hydrocarbons to make the end products. Adding atomically-bonded oxygen catalysts will speed the bioremediation processes when aerobic organisms are present.

Carbon is the most basic element of living forms and is needed in greater quantities than other elements. In addition to hydrogen, oxygen, and nitrogen it constitutes about 95% of the cell weight. Phosphorous and sulfur contribute with 70% of the remainders. A typical bacterial cell is 50% carbon, 14% nitrogen; 3% phosphorus; 2% potassium; 1% sulfur; 0.2% iron, and 0.5% each of calcium, magnesium, and chloride. Therefore all organisms also require nutrients containing some form of nitrogen, hydrogen, oxygen, sulfur, phosphorus, and numerous other trace elements even though the primary building blocks are carbon. The addition of inorganic nutrients in a formulation that will make available the necessary elements to assure complete nutrition to the growing microbe population is essential. The nutritional requirement of carbon to nitrogen ratio is 10:1, and carbon to phosphorous is 30:1.

A certain amount of heat is necessary for chemical reactions, even when broken down by enzymes to proceed at a rate fast enough to sustain life. The rate of most enzyme-catalyzed reaction (breaking the substrate down) increases by a factor of 2 for every 10 degrees (Celsius) increase in temperature, up to the temperature at which the particular enzyme begins to deteriorate. Temperatures near or below freezing will cause the microbes to go dormant and therefore bioremediation will cease until warming occurs. This does not destroy the bioremediation capability permanently. Enzymes simply cannot be exuded from the cell into solid water (ice). Bioremediation recommences as warmer temperature is achieved. Temperatures sufficiently high to kill the microbes (starting at 140 degrees F.) will effectively stop the bioremediation process but this is not expected in most environment applications.

V. BIOREMEDIATION OF SUGAR INDUSTRY EFFLUENT

Bioremediation of sugar industry effluent are generally classified as ex situ application of biostimulation, since microorganisms and its enzymes do not exist naturally in the wastewater. Microorganisms are added to the effluent, which, through its series of metabolism reactions, oxidizes complex, organic pollutants present in the effluent into simpler, less harmful, organic compounds.

Bioremediation, in its application to treatment of wastewater, is commonly known as biotreatment, encompassing all wastewater treatment technologies that use microorganisms for degradation. It includes the use of bioreactors, such as activated sludge process and anaerobic digesters; phytodegradation and rhizofiltration, such as reed bed system; and land application systems.

Biotreatment of sugar effluent can be accomplished using ponds. Ponds are relatively easy to build and manage, can accommodate large fluctuations in flow, and can also provide treatment that approaches conventional systems (producing a highly purified effluent) at much lower cost. It is the economics that drives many managers to decide on the pond option. The actual degree of treatment provided depends on the type and number of ponds used. Ponds can be used as the sole type of treatment or they can be used in conjunction with other forms of wastewater treatment (i.e., other treatment processes followed by a pond or a pond followed by other treatment processes).

Engineering a biotreatment system requires not only the establishment of efficient unit processes and unit operations, but entails a wider understanding of microbiology in interpreting process parameters, to achieve a more efficient treatment system. The efficiency of biotreatment depends largely on the activity of the microbial population involved in the process, hence, efficient operation of the same, requires knowledge on interpreting process parameters at the microbial level.

VI. BIOLOGICAL ASPECTS AND PROCESSES

Uncontrolled bacteria in treatment systems produce an endless variety of problems including equipment and product damage. It should be noted that all the biological processes used for the treatment of wastewater are modelled from naturally occurring processes. It also should be noted that by controlling the environment of microorganisms, the decomposition of wastes is speeded up. Regardless of type of waste, the biological treatment process consists of controlling the environment required for optimum growth of the microorganism involved.

a. Growth Cycles

All organisms follow a basic growth cycle that can be shown as a growth curve. This curve occurs when the environmental conditions required for the particular organism are reached. It is the environmental conditions (i.e., oxygen availability, pH, temperature, presence or absence of nutrients, presence or absence of toxic materials) that determine when a particular group of organisms will predominate. This information can be very useful in operating a biological treatment process.

b. Common Operational Control Levels

Control levels can be defined as the upper and lower values for a process control variable that can be expected to produce the desired effluent quality.

Several major factors should be considered when establishing control levels for the activated sludge system. These include the following:

i. Influent characteristics

A major area to consider when evaluating influent characteristics is the nature and volume of industrial contributions to the system. Waste characteristics (BOD, solids, pH, metals, toxicity, and temperature), volume, and discharge pattern (continuous, slug, daily, weekly, etc.) should be evaluated when determining if a waste will require pre-treatment by the industry or adjustments to operational control levels.

ii. Industrial contributions

One or more industrial contributors produce a significant portion of the plant loading (in many systems). Identifying and characterizing all industrial contributors is important. Remember that the volume of waste generated may not be as important as the characteristics of the waste.Extremely high-strength wastes can result in organic overloading and poor performance because of insufficient nutrient availability.

A second consideration is the presence of materials that even in small quantities are toxic to the process microorganisms or create a toxic condition in the plant effluent or plant sludge.

Industrial to a biological treatment system should be thoroughly characterized prior to acceptance, monitored frequently, and controlled by implementation of a pre-treatment program.

iii. Process side streams

Process sidestreams are flows produced in other treatment processes that must be returned to the wastewater system for treatment prior to disposal.

Testing these flows periodically to determine both their quantity and strength is important. In many treatment systems, a significant part of the organic and/or hydraulic loading for the plant is generated by sidestream flows. The contribution of the plant sidestream flows can significantly change the operational control levels of the activated sludge system.

iv. Seasonal variations

Seasonal variations in temperature, oxygen solubility, organism activity, and waste characteristics may require several normal control levels for the process. For example, the aeration rate may be controlled by the mixing requirements of the system during the colder months and by the oxygen demand of the system during the warm months.

v. Required effluent quality

c. Visual Indicators

Process operators are required to monitor certain observations of treatment processes to ensure optimum performance and make adjustments when required.

i. Turbulence

Normal operation of an aerated ponds includes a certain amount of turbulence. This turbulent action is required to ensure a consistent mixing pattern. Whenever excessive, deficient or non-uniform mixing occurs, adjustments may be necessary to airflow, or diffusers may need cleaning or replacement.

ii. Surface Foam and Scum

The type, color and amount of foam or scum present may indicate the required wasting strategy to be employed.

Type of FoamIndicationAdjustment

Fresh, crisp, white foamWhite foam are usually associated with processes producing an excellent final effluentNone. This indicates a normal operation

Thick, greasy, dark tan foamIndicates an old sludge that is overoxidized, has a high mixed liquor concentration and has a waste rate that is too highMore wasting is required

White billowing foamIndicates a very young, underoxidized sludgeLess wasting required

iii. Sludge Color and Odor

Though not as reliable indicator of process operations as foam, sludge colors and odor are useful indicators that indicates the following:

ObservationsIndication

Chocolate brown or earthy odorNormal operation

Light tan or brown or no odorIndicates sand and clay from infiltration or inflow. Indicates also a very young sludge, hence need to decrease wasting

Dark brown or earthy odorIndicates old sludge and high solids. Increase wasting

Black color or rotten egg odorIndicates septic conditions, low DO concentration, and an airflow rate that is too low. Increase aeration

iv. Sludge Characteristics

ObservationsIndication

Sludge bulking

Occurs when solids are evenly distributed throughout the tank and leaving over the weir in large quantities

Sludge Solids Washout

Sludge blanket is down, but solids are flowing over the effluent weir in large quantities. Control tests indicate good quality sludge.

Clumping

Large clumps or masses of sludge (several inches or more) rise to the top of the settling tank

Ashing.

Fine particles of gray to white material flowing over the effluent weir in large quantities

Straggler floc Small, almost transparent, very fluffy, buoyant solids particles (1/8 to 1/4 in. diameter rising to the surface). Usually is accompanied by a very clean effluent. New growth is usually most noted in the early morning hours. Sludge age is slightly below optimum.

Pin flocVery fine solids particles (usually less than 1/32 in. diameter) suspended throughout lightly turbid liquid. Usually the result of an overoxidized sludge.

VII. REFERENCES

Spellman, Frank R., Handbook of Water and Wastewater Treatment Plant Operations, CRC Press LLC, 2003

Tiwari, B.D., Sewage Pollutin and Microbiology, Swastik Publishers & Distributors Delhi, 2009

Sharma, Shilpi, Bioremediatin: Features, Strategies and Applications, Asian Journal of Pharmacy and Life Science, Vol. 2 (2), June, 2012

Saranraj, P. and Stella, D., Effect of Bacterial Isolates on Reduction of Physico-Chemical Characteristics in Sugar Mill Effluent, International Journal of Pharmaceutical & Biological Archives, 2012