Process Instrumentation for Organic Waste Anaerobic Digestion

The market for AD in Organic Waste has been growing slowly but steadily in the last 5 years not only in Ontario, or the whole of Canada, but in the USA and Europe. It has expanded in the following categories;

  1. Agricultural
  2. Dairies
  3. Fresh produce markets
  4. Deli’s/Restaurants
  5. Municipal
  6. Cruise lines
  7. Brewery and Wineries
  8. Zoos/Race Track

Except for those plants intended for Agricultural, licenses and permits to construct these kind of commercial AD plants are becoming harder to obtain. In Ontario alone, the MOE’s Certificate of Approval is the longest in processing, that would involved town hall meetings, liaison with the public, building permit, zoning, connection to grid agreement with OPG or gas pipeline connection with Union Gas or Enbridge, securing supplies of feedstock.

The main goal of the AD Process is to effectively capture methane gas and carbon dioxide from escaping to the atmosphere thus reducing green house gas emissions, the other by-products are power co-generation  and/or  liquefied compressed natural gas, and soil conditioning compost.

The intricate process is dependent on the use of Process Instrumentation that operates, controls and monitors every details of the operation. A good example is that of Halton Recycling operation in Newmarket. It has a design capacity to process up to 100,000 tons of SSO per year, 35,000 cu. M. Of liquid waste, with an electrical out put of 2.2 MW-hr and compost output of 35,000 tpy.

Noel Moya, president of Fluidyne, states that “A well programmed process instrumentation could cover from measurement of the incoming and outgoing loads, batch and continuous method that includes all equipment, amp-power draw, process temperature, pH, time, set-points, flow/pressure/vacuum/speed measurements from pumping and compressing equipments, combined heat and power co-generation performance, kw-hr production, biofilter performance, and humidity. It could also be combined with other program for weather monitoring, odor control sensors, security , laboratory test results such as BOD, COD, VFA’s, TS, VS, Feed”.

Rate, sanitary sewer discharge. Overall, this instrumentation could also perform a mass balance and fault finding program with an early warning signal for possible problems. It also can be coded against tampering.

Such programs typically take over 2 years to master. If enforced properly, the operator would be guided from the following common mistakes:

  1. Irregular loading rates
  2. Guess work on VFA Loading
  3. Acidification, an AD upset condition – foaming
  4. Unmonitored Influent/Effluent measurements on pH, temp., TS, VS, VFA, Loading rates, COD degradation
  5. Unregulated Process Water Return flow measurement
  6. Uncontrolled HRT/SRT
  7. Gas flow measurement leaks causing odor
  8. Moisture content on gas produced

Noel goes on to explain that most of the problems encountered in operating an AD facility with composting is in the location in the neighbourhood. The stakeholders always perceivethat your plant will produce odors that could potentially affect the value of their living condition.  No matter how perfect  the air balance and the size of the odor control equipments, such as the Biofilter, you will always receive a nuisance complaint even at the best weather condition favourable to your plant operation.

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