1. ANAEROBIC DIGESTION OF FISH SLUDGE FOR BIOGAS PRODUCTIONBY
NETSHIVHUMBE RUDZANI
Supervisor : Dr N.J Goosen
Co-supervisor : Prof J Gorgens
Prof N.S Mamphweli
Dr F.D Faloye

2. BACKGROUND
Recirculation aquaculture systems (RAS) are considered as sustainable and environmental friendly aquaculture systems capable of meeting the growing demand of seafood for human consumption.
Source (FAO, 2015)
South Africa produces tons annually (FAO, 2015).
It is estimated that 1000kg of fish production from the RAS generates about 375kg of dry organic solid waste (Tal et al.,2009).
However, RAS produces large quantities of waste sludge from uneaten feed and fish faeces (Mirzoyan et al.,2008).

3. BACKGROUND
Scheme of a Recirculating Aquaculture System (adapted from Mirzoyan et al.,2008)
proper management in order to prevent environmental impacts such water pollution and eutrophication, emission of unpleasant odours, high content of salinity, leachate with a high polluting potential
Due to high content of salinity of sludge from saline aquaculture limit sludge management options of landfill, as discharge it into the environments it can lead to salinization of soils.
Fish production tank
oxygenation
Nitrification
Biofilter
Biogas
Mechanical filtration
Sludge Disposal unit (AD)
Backwash
Sedimentation solid separation
Sludge

4. BACKGROUND
Anaerobic digestion (AD) is biological degradation of organic matter by microbes under anaerobic conditions (Mirzoyan et al.,2008).
Biogas resulting by anaerobic digestion is a source of renewable energy because it replaces fossil energy
AD has been considered as an alternative method to reduce the amount of organic waste in the environment before their disposal (Eiroa et al., 2012).
Benefits of AD of organic waste
Recover bio-energy (methane)
Reduction of methane emission
Reduce waste management
Reduction of pollution
Bio-fertilizer

5. BACKGROUND Anaerobic digestion process
Anaerobic digestion process and reactions-diagram (Gujer and Zehnder, 1983)

6. BACKGROUND Factors affecting the anaerobic digestion process:
Temperature : Mesophilic (35-37°C)
Thermophilic (45-55°C)
pH and alkalinity: optimal between 6.8 to 7.2 (McCarty, 1964)
C/N ratio : optimum (20-30)
Substrate loading (TS 6-10%)
Mixing : prevents sedimentation and foaming of dead zones in the reactor.

7. RESEARCH RATIONALE Composition of fish sludge
Fish sludge waste from aquaculture is rich in organic matter such as nitrogen (Mirzoyan et al.,2008).
Biodegradable
High volatile solids (60-90%) (Mirzoyan et al.,2008).
High moisture content
Potential problems of fish sludge as a substrate for biogas production
Low C/N ratios of the sludge
Total solids content (low)
High concentration of metals
High salinity of the sludge
Therefore, in order to overcome these limitation, it important to have a carbon-rich co-substrates that will balance the nutrients.
Low methane yield

8. RESEARCH RATIONALE
Anaerobic Co-digestion is the digestion of two or more substrates simultaneously in the same digester to make a process more stable (Mshandete et al.,2014).
Advantages of co-digestion (Mata-Alvarez.,2014)
Improved nutrient balance for an optimal digestion
Dilution of inhibitory substance
Enhance biogas production
Improve the process stabilization
However, the ratio of fish sludge with other co-substrates must be balanced in order to achieve an optimum biogas yields.

9. CURRENT RESEARCH
Aim
The current study aim to optimise the biomethane production from fish sludge originating from RAS using anaerobic digestion.
Research objectives
To determine the chemical compositions of fish sludge from a RAS and it’s suitability for anaerobic digestion.
To optimise operating parameters to maximize the methane in the biogas.
To identify and evaluate suitable substrates for anaerobic co-digestion, in order to increase biomethane yield.

10. MATERIALS AND METHODS Samples Collection Inoculum
The inoculum samples will be obtained from an active digester running in Stellenbosch University lab.
Substrates
Fish sludge will be collected from the RAS at the experimental farm at Stellenbosch University.

11. Fish sludge and inoculum Anaerobic co-digestion trial
METHODOLOGY
Fish sludge Analysis
Analytical methods
Elemental analyser
C, H, N, S, O content
Colorimetric analysis
Chemical oxygen demand (COD)
Alkalinity tritation method
Alkalinity and pH
Proximate analysis
Moisture content, TS, VS.
BMP testing
(AMPTS II)
Characterisation
(TS, VS, C/N, pH)
Collection
Fish sludge and inoculum
Anaerobic co-digestion trial
(Mixture design)

12. Anaerobic co-digestion Anaerobic co-digestion
METHODOLOGY
Process of optimisation
Co-substrates
Fish sludge
Characterisation
(TS, VS, C/N, pH)
Anaerobic co-digestion
(AMPTS II)
Anaerobic co-digestion
(30L digester)
CSTR
Characterisation of
Digestate

13. EXPECTED OUTCOMES
Suitable co-substrate of anaerobic digestion of fish sludge
Generate optimal biomethane yield
Possibility of integration of large-scale anaerobic digestion bioreactor in the RAS.
Provide information on quality of digestate

14. REFERENCES
Mirzoyan, N., Parnes, S., Singer, A., Tal, Y., Sowers, K., Gross, A., Quality of brackish aquaculture sludge and its suitability for anaerobic digestion and methane production in an upflow anaerobic sludge blanket (UASB) reactor. Aquaculture 279, 35–41.
Eiroa, M., Costa, J.C., Alves, M.M., Kennes, M.C Evaluation of the biomethane potential of solid fish waste. Waste Management 32 , 1347–1352
Gujer, W., and Zehnder, A. J. B. (1983). Conversion processes in anaerobic digestion. Water Science and Technology 15,
Mshandete, A, Kivaisi, A, Rubindamayugi, M and Mattiasson, B. (2004). Anaerobic batch co-digestion of sisal pulp and fish wastes. Bioresource Technology 95(1):19-24.
Mata-Alvarez, J. Mace, S., Llabres, P. (2000). Anaerobic digestion of organic solid wastes. An overview of research achievements and perspectives. Bioresource Technology 74: 3-16.
McCarty, P.L., (1964). Anaerobic waste treatment fundamentals, part III: Toxic materials and their control. Public Works 95 (11), 91–94
FAO The state of world fisheries and aquaculture. Rome: Food and Agriculture Organization of the United Nations. Fisheries Department

15. ACKNOWLEDGMENT
This study funded by the Centre for Renewable and Sustainable Energy studies

16. Thank you