N. Defoer & H. Van Langenhove Research Group of Environmental Organic Chemistry and Technology, Ghent University

Transcription

1 N. Defoer & H. Van Langenhove Research Group of Environmental Organic Chemistry and Technology, Ghent University

2 Introduction biological waste treatment is a growing sector in Europe 30% of urban waste/industrial residuals is biodegradable or 60 million tons/year Flanders (2000): tons greenwaste tons VFG (vegetable, fruit and garden waste) Consequence of this growth: odour is becoming an increasingly sensitive issue!

3 Introduction Aim of this presentation: Giving an overview of the present knowledge on odour emissions and possible reduction techniques at composting facilities

4 Odour generation Important mechanisms in odour generation: anaerobic conditions high temperatures stripping

5 Odour generation 1. anaerobic conditions aerobic: organics + O 2 CO 2 + H 2 O anaerobic: instead of O 2 other electronacceptors like NO 3-, SO 4 2-, oxidized matter and CO 2 results in formation of N 2, H 2 S, organic sulphur compounds, reduced organic compounds and methane efficient aeration, optimal moisture content and appropriate porosity will contribute to less odour production Note: Anaerobic microsites are hard to avoid in practice!

6 Odour generation 2. High temperatures Development of typical process phases with own temperatures and production of specific odorants mesophilic startphase: biogenic odour components (terpenes) selfheating phase: volatile biogenic odours thermophilic phase: decrease of biogenic odours abiogenic odours by pyrolyse, auto-oxidation, Maillard reactions maturation phase: decline in temperature, decrease of microbiological activity

7 Odour generation Activity of thermophilic organisms optimal at 52 to 60 C Macgregor et al. (1981), Finstein et al. (1986): reduction in odour production when T < 60 C Miller (1993), Toffey et al. (1995), Hentz et al. (1996): increasing odour emission at increasing composting temperatures

8 Odour generation 3. Stripping Aeration of biowaste improves input of oxygen promotes output of volatile odorous substances

9 Odour sources Flanders: 2 types of waste are composted separately VFG waste (vegetable, fruit & garden waste) composting in closed buildings greenwaste (organic waste from gardens, parks & roadsides) composting outside

10 Odour sources Continuous odour sources - storage of waste - composting process - leachate Discontinuous odour sources - dumping of waste - shredders, mills, - turning and moistening of compost - sieving - digging up compost

11 Odour sources Diffuse odour sources leachate, open hall doors, cracks, failure to properly clean facility areas, Kuchta (1994): diffuse odour sources can be up to 10% of total odour emission at composting facilities

12 Odour sources Bidlingmaier (1993) Odour emission (ou/h 10 4 ) Composting stage Air flow (m 3 /h) Receiving area Pretreatment Composting area -sucking -blowing Storage Final treatment composting area (including turning) most important odour source immediately prior to turning: 1000 ou.m -3 during turning: 5000 ou.m -3 relative values more important than absolute values

13 Odour sources TNO (1994) research at greenwaste composting facilities with different turning frequencies turning most important odour source followed by continuous emission of composting piles and storage of biological waste contribution of different sources (in percentage) dependent on method of composting

14 Factors influencing odour emission History of waste storage, frequency and way of collecting material too long in collection containers trash and putrefying odours De Bo & Van Langenhove (1999): one week storage of material that was collected every two weeks gave rise to an odour emission of 2 to 6 times higher Conclusion: it is really important to handle the waste the same day as it is received!

15 Factors influencing odour emission Feed composition high levels of specific feed like grass can be problematic grass fraction > 10%: odour problems are possible mechanism: high grass levels (nitrogen source) no lack of nitrogen higher rate of oxygen depletion anaerobic conditions Possible solution: addition of grass in phases during the composting process

16 Factors influencing odour emission Seasonal influence cumulation of different effects: - higher waste supply (from June to September supply 2 or 3 times as high as in January and February) - feed composition (more grass) - higher temperatures higher odour emission during spring/summer

17 Factors influencing odour emission Moisture content one of the most common factors leading to anaerobic conditions moisture < 35-40%: reduction of decomposition upper limit varies with different materials (function of particle sizes and structural characteristics) for most compost mixtures: 55-60% is recommended

18 Odour reduction techniques Turning frequency turning releases odorous compounds trapped within piles lack of turning allows anaerobic conditions increases severity of odours when piles are eventually disturbed Defoer & Van Langenhove (2000): research on the influence of turning frequency on odour emission at 3 greenwaste composting plants with different turning frequencies ( plant A: every 6 weeks, plant B: every week, plant C: every 8 weeks)

19 Odour reduction techniques Turning frequency RESULTS - odour emission high and nearly the same during first 10 days - afterwards fast decline to the same continuous odour emission - peak emissions after every turning were lowest for plant B with the highest turning frequency

20 Odour reduction techniques Turning frequency CONCLUSIONS - a complete odour balance could not be made - the plant with the highest turning frequency had the lowest odour emission - other factors (height of compost piles, turning equipment, ) could have played a role

21 Odour reduction techniques Aeration inadequate oxygenation (aeration) leads to development of anaerobic conditions active aeration has pronounced effect on both rate of composting and odour production Influence type of aeration research of Bidlingmaier (1993) sucking aeration: ou.h -1 blowing aeration: ou.h -1

22 Odour reduction techniques Odour masking overpowering of the odorous molecules with stronger, more pleasant molecules Defoer & Van Langenhove (2000): sniffing team measurements around a greenwaste composting plant with and without odour masking products - large variation in the results (from -5 to +73% reduction with a mean value of 17%) - soap odour is also annoying - no ecologically sound reduction technique

23 Odour reduction techniques Air treatment air from closed buildings can be removed by ventilation used as process air for aerating compost piles (odour reduction) odour removal by chemical or biological treatment biological treatment is the most cost-efficient technique in Flanders used by all VFG composting facilities

24 Odour reduction techniques Air treatment Defoer & Van Langenhove (2000): monitoring campaign of biofilters at 5 Flemish aerobic VFG composting plants - 3 of the 5 biofilters: VOC removal efficiency > 94% - 1 biofilter lower efficiency of 80% due to low influent concentrations - 1 biofilter VOC removal efficiency of only 64% (reason was not clear)

25 Odour reduction techniques Air treatment Note: results were expressed in VOC removal efficiency but Defoer et al. (2002) found a good correlation between odour and VOC concentration for the effluent of biofilters at VFG composting plants biofiltration is a reliable technique for odour removal at composting facilities

26 Final conclusion considerable research on odour production has been done importance of factors like turning frequency and aeration are difficult to describe quantitatively effects of odour masking products are ambiguous VFG composting: biofiltration is a reliable technique for odour removal greenwaste composting: not in closed buildings biofiltration not possible other methods like adaptation of aeration and turning frequency must offer a solution

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