Research Topic: Effect of Lipid Inhibition in Anaerobic Wastewater Treatment: A Case Study Using Desiccated Coconut Wastewater

1. Effect of Lipid Inhibition in Anaerobic
Wastewater Treatment
A Case Study Using Desiccated Coconut
Wastewater
Presented by : Kasun Samarasiri
Supervised by : Dr. P.G. Rathnasiri
IESL Annual Sessions, Sri Lanka.
18th of October, 2016.

2. CONTENT
1. Introduction
2. Research Problem
3. Lipid Inhibition
4. Strategies to Overcome Lipid Inhibition
5. Case Study
6. Results and Discussion
7. Further Experiments

3. INTRODUCTION
• Desiccated coconut (DC) industry is one of the largest export
industries in Sri Lanka.
• DC is produced by drying the white coconut kernel.
• DC production process consists of various unit operations such as de-
shelling, de-husking, paring, splitting, washing, inspection,
pasteurization, sterilization, size reduction, drying, screening, grading
and packaging, etc

4. INTRODUCTION
Wastewater generation in the DC production process
• Wash water is generated during paring and washing process
• Coconut water is generated during the splitting process
• Condensate loss is generated during the sterilization process
Successful wastewater treatment facility in a DC processing plant

5. RESEARCH PROBLEM
• Oily effluents often cause problems such as clogging of wastewater
pipelines, biomass washout and depletion of dissolved oxygen in
surface water bodies.
• DC wastewater (DCWW) typically consists of wash water, coconut
water and condensate loss from sterilization in the ratio of 16:4:1.
• DCWW consists of high concentration of biodegradable
carbohydrates(sugars) and lipids.
• High concentrations of lipids will lead into process instability in
anaerobic reactors resulting an inefficient effluent treatment.

6. RESEARCH PROBLEM
Typical characteristics of DCWW (CEA Report on DC industry 1993)
SLS standards for discharge of wastewater into inland surface waters
Parameter Range
pH at 25°C 4.0 – 5.5
COD (mg/l) 4000 – 8000
BOD (mg/l) 1000 – 5000
Total lipids (mg/l) 4000
Parameter Range
pH at 25°C 6.0 – 8.5
COD (mg/l) 250
BOD (mg/l) 30
Total lipids (mg/l) 10

7. LIPID INHIBITION
• The metabolism pathway of anaerobic digestion is followed by
hydrolysis, acidogenesis, acetogenesis and methanogenesis.

8. LIPID INHIBITION
• Lipid is breakdown into lipid micelles, glycerol and fatty acids by
hydrolytic anaerobes.
• Fatty acid transport into the cell through phospholipid cell
membranes occurs by adsorption, transmembrane movement, and
desorption.

9. LIPID INHIBITION
Because of their low solubility in water phase and high
hydrophobicity, fatty acids bind rapidly the phospholipid cell
membranes of anaerobes.
The presence of long chain fatty acids (LCFA) is reported as the main
cause of inhibition in anaerobic digestion of oily effluents.
• The energy content in LCFA is very higher and molecules are larger so
that anaerobes are less likely to absorb it to gain energy
• Remaining LCFA will attach around the microbial cell membranes
• LCFA limit the mass transfer between the microorganisms and the
medium

10. STRATEGIES TO OVERCOME LIPID INHIBITION
• Effect of Operating Temperature - psychrophilic, mesophilic,
thermophilic and hyperthermophilic
• Effect of Feeding Sequence - batch feeding, continuous feeding,
intermittent feeding
• Effect of Saponification - KOH, NaOH and Ca(OH)2
• Effect of Co-digestion - carbohydrates, proteins, lipids and minor
nutrients
• Effect of Enzymatic Pre-treatment - lipases
• Effects of Absorbent Addition - bentonite, calcium chloride, titanium
dioxide and zinc oxide
• Sonication, Ozonation and Two-Stage Digestion

11. CASE STUDY
Sample Collection
• Drag samples were collected from the inlet and outlet of the
anaerobic reactor at a typical DC wastewater treatment plant.
• Samples were brought to the laboratory using glass vials inside an ice
chest and stored at 4°C until taken for analysis
Analytical Methods
• COD analysis was conducted by standard closed reflux, titrimetric
method. (Hach DRB200 - COD reactor)
• pH analysis was conducted by benchtop pH meter. (Eutech CyberScan
pH 510 - pH meter)

12. CASE STUDY
COD Variations of inlet and outlet of anaerobic reactor and variations
of COD removal efficiency.

13. CASE STUDY
pH Variations of inlet and outlet of anaerobic reactor and Oil and
Grease variations from the previous records.

14. RESULTS AND DISCUSSION
Summary of the Analytical Measurements.
Parameter Mean Standard Deviation
COD in (mg/l) 6017.49 1276.63
COD out (mg/l) 2518.95 2096.87
pH in 5.92 1.14
pH out 7.09 0.16
COD Removal Efficiency (%) 62.69 27.87
Oil and Grease Content (g/l) 4.42 3.14

15. RESULTS AND DISCUSSION
COD removal efficiency of the anaerobic reactor drastically dropped
down after a certain threshold point of COD inlet level above 6,500
mg/l from 90% (at COD – 5000mg/l) to 30% (at COD – 7000mg/l).
The oil and grease content varied from 2 g/l to 11 g/l which could
exceed the average inhibitory concentrations of oil and grease (1 g/l to
5 g/l) of other anaerobic reactors mentioned in the literature.

16. RESULTS AND DISCUSSION
• Higher shock loadings reduce the efficiency of the anaerobic
treatment process.
• Anaerobic reactor failure occurs due to the accumulation of lipids.
• Previously mentioned strategies such as saponification with KOH,
NaOH and Ca(OH)2, co-digestion of lipids, enzymatic pre-treatment
with lipases, absorbent addition such as calcium chloride, bentonite,
titanium dioxide, zinc oxide, zeolite, sonication with ultrasonic
homogenizers, ozonation and two-stage digestion with two series
reactors operating at different conditions can be applied to overcome
lipid inhibition.

17. FURTHER EXPERIMENTS
Further experiments should be conducted to evaluate the most
practical treatment strategy by considering,
• Environmental factors - Higher treatment efficiency enhancement.
• Environmental factors - Treatment efficiency changes at different
shock loadings (COD/O&G).
• Industrial factors - Land requirement, technology requirement,
equipment requirement and other practical factors of the treatment
strategy.
• Economical factors - Capital investment, operational costing and
maintenance costing of the treatment strategy.

18. QUESTIONS?

19. QUESTIONS?