Introduction

Whole Systems Approach to Ecological Design

Appropriate Technology: Water

Organic Agriculture and Local Food

Appropriate Technology: Energy

Green Building & Retrofitting
Appropriate Technology: Water
Whole Systems Approach to Water Constructed Wetlands Treatment Rainwater Harvesting Lagoon and Tank Based Treatment

Aerobic digestion

The removal of organic carbonaceous material from wastewater is measured as a reduction in the biochemical oxygen demand (BOD5) in the wastewater.  There are four basic steps in the removal of organic material, or reduction in BOD, from the wastewater stream, including:

  • The solubilisation of large organic molecules;
  • The uptake of organic matter (small compounds) from the wastewater by microorganisms;
  • The conversion of organic matter to cellular matter (bacteria) and CO2 through the microorganism’s metabolic processes;
  • The transformation of carbon up a food chain and into CO2 through predation, feeding, and metabolism by protozoans, rotifers, and other microorganisms.

In order to breakdown large organic molecules, bacteria often produce exoenzymes that breakdown solids outside of the organism’s body.  Following breakdown of solids, heterotrophs convert carbonaceous BOD to bacterial biomass and CO2 (50-80%).  Bacteria that are often found completing these processes include Aerobacter aerogene, Bacillus subtilis, Cellulomonas biazotea, Pseudomonas denitrificans, P. Stutzeri, Nitrobacter winogradskyi, Rhodopseudomonas palustris, and Nitrosomonas sp.  These organisms will naturally seed themselves into the wetland from the environment.  Breakdown (solubilisation) of solids is a precursor for nitrification, which requires oxygen and an inorganic carbon source (Ehrlich et al. 1997).  The transfer of organic matter to the cell and its subsequent conversion into cell matter generally occurs in the aerobic zone of a constructed wetland.