and Microbiological Parameters Influencing the Small-scale In-vessel - - PowerPoint PPT Presentation

Investigation of the Physical, Chemical and Microbiological Parameters Influencing the Small-scale In-vessel Composting of Food Waste

• D. Orthodoxou, T.R. Pettitt, M. Fuller, M. Newton, N.

Knight, S.R. Smith

CYPRUS 2016

Food Waste (FW): a challenging feedstock

■ Needs bulking agents, otherwise it becomes highly homogeneous ■ High moisture content ■ Often very acidic ■ Collection in closed containers can lead to anaerobic conditions, further lowering pH ■ Must be treated in an enclosed environment, specified time- temperature conditions

The role of VFAs in FW composting

■ Initial decrease in pH is often observed after FW addition to IVC. In severe cases this can lead to significant decline in temperature and malodours ■ VFAs in compost mixture play key role in regulating pH during mesophilic phase ■ Acidic compost mix (pH<6)  undissociated VFAs  inactivation of aerobic microorganisms  accumulation of VFAs  further acidification ■ Mesophilic aerobes are more acid tolerant than thermophilic

• rganisms

■ Maintaining the compost temperature below 46ºC until the pH value increases above pH 6.5, allows aerobic organisms to degrade VFAs, thus shortening the mesophilic phase and increasing the composting temperature in a shorter period of time.

In-vessel FW composting at the Eden Project

■ FW shredded to 20mm particle size ■ Retention time between 60 and 110 days (depending on feeding rate)

Feedstock

Feeds eedstock

• ck

pH pH Chara ract cteris eristics tics Food Waste (FW) 4.0-4.4 after shredding High MC, little porosity Green Waste (GW) 6.0-8.0 Increases C/N ratio. Adds microbial population Corrugated Board Dust (CBD) 8.0 Low MC (~11%). Drying agent Sawdust (SD) 5.6-5.8 Drying agent Sawdust Pellets (PEL) 4.7 Low MC (~15%). Expands

• n rehydration, increases

free air space Finished Compost (FC) 7.5-8.5 Drying agent. Adds thermophilic organisms

Eight week feedstock management strategy

Inp nput (kg) g): Week 1 2 3 4 5 6 7 8 FW FW 572

• 14

224 279 GW GW 208 300 101 197 84 350 205 84 FC FC 80 172 681(565)

• 115

47 CBD 99 125 34 132 119

• SD

SD

• 5

22

• PEL
• 16
• 242

30 30 Tot

• tal

al Inp nput ut: 959 602 838 345 203 606 574 440 Tot

• tal

al Output put (kg) g): 194

• (55)*

388 179 579 189

• * Value in brackets represents the material removed from the discharge end of the vessel and recycled to the feed end.

Changes in temp., moisture content and pH

Hatch 1

20 25 30 35 40 45 50 55 60 65 70 2

• J

u n 5

• J

u n 1 1

• J

u n 1 6

• J

u n 2 2

• J

u n 2 6

• J

u n 1

• J

u l 7

• J

u l 1 3

• J

u l 1 7

• J

u l 2 3

• J

u l Sampling Date Sample Temperature ( oC) / % Moisture Content 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 pH Temperature Moisture Content % pH

Hatch 2

20 25 30 35 40 45 50 55 60 65 70 2-Jun 5-Jun 11-Jun 16-Jun 22-Jun 26-Jun 1-Jul 7-Jul 13-Jul 17-Jul 23-Jul Sampling Date Sample Temperature ( oC) / % Moisture Content 3.0 4.0 5.0 6.0 7.0 pH Temperature Moisture Content % pH

Hatch 3

20 25 30 35 40 45 50 55 60 65 70 02-Jun 05-Jun 11-Jun 16-Jun 22-Jun 26-Jun 01-Jul 07-Jul 13-Jul 17-Jul 23-Jul Sampling Date Sample Temperature ( oC) / % Moisture Content 4.0 4.5 5.0 5.5 6.0 pH Temperature Moisture Content % pH

Hatch 4

20 25 30 35 40 45 50 55 60 65 70 02-Jun 05-Jun 11-Jun 16-Jun 22-Jun 26-Jun 01-Jul 07-Jul 13-Jul 17-Jul 23-Jul Sampling Date Sample Temperature ( oC) / % Moisture Content 4.0 5.0 6.0 7.0 8.0 9.0 10.0 pH Temperature Moisture Content % pH

The effect of MC and pH on the temperature of the compost mixture

A Temp oC = 103.2 - 1.18 MC R 2 = 0.75 P < 0.001 20 25 30 35 40 45 50 55 60 65 20 25 30 35 40 45 50 55 60 65 % Moisture Content Sample Temperature ( oC) B Temp oC = 25.81 + 18.12 pH - 1.03 pH2 R 2 = 0.84 20 25 30 35 40 45 50 55 60 65 3.5 4.5 5.5 6.5 7.5 8.5 9.5 pH Sample Temperature ( oC)

The effect of % moisture content on pH

% Moisture Content

20 30 40 50 60 70

pH

3 4 5 6 7 8 9 10

Interstitial gas concentrations

Relationship between temperature and C02 and temperature and 02

A %CO2 = 15.0 + 0.65 Temp oC R 2 = 0.66 P < 0.001 5 10 15 20 25 30 35 30 35 40 45 50 55 60 65 70 Compost Temperature (oC) % CO2 B %O2 = 32.1 - 0.56 Temp oC R 2 = 0.69 P < 0.01 5 10 15 20 25 30 35 40 45 50 55 60 65 70 Compost Temperature (oC) % O2

Conclusions

■ The rapid biodegradation of FW makes its composing susceptible to acid accumulation and pH decline. ■ The results show that process acidification is highly sensitive to increasing MC. ■ Possible reason: MC influences the thermodynamic balance of the process. A wet mixture leads to greater heat losses, causing a decline in temperature and a decline in VFA metabolism. Feedback mechanism leading to more VFA accumulation and pH reduction  microbial toxicity  process inhibition. ■ MC between 41-48% were associated with a marked transitional increase in compost pH above 6.0 and a concomitant rise in temperature to thermophilic values ■ Moisture contents over 48% caused severe acidogenesis and mesophilic temperatures ■ Under the conditions of this investigation the upper critical MC for in-vessel composting of food waste was 40% (whereas the recommended MC for composting is in the range of 40-60%).

Orthodoxou, D., Pettitt, T.R., Fuller, M., Newton, M., Knight, N., Smith, S.R. (2015). An Investigation of Some Critical Physico-chemical Parameters Influencing the Operational Rotary In-vessel Composting of Food Waste by a Small-to-Medium Sized Enterprise. Waste and Biomass Valorization, 6 (3)

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