dog food is a good one: 1 lb dog food= about 1 lb BOD. Keep in mind the nitrifiers are going to use inorganic carbon and the organic carbon is for your heterotrophic bacteria.

Can I use starch? or water from rice or potato? as we prefer something cheaper too

jeffryy:

What type of wastewater are you trying to test ? If industrial, then mimic the major type(s) of carbon present. Municipal synthetic wastewater can be more difficult. This is because most of the readily degradable carbon is gone by the time the wastewater reaches the treatment plant. Glucose, sucrose and starch are not good choices as these select specific floc-forming bacteria maybe not significant if municipal wastewater is actually used. This in turn skews your experimental results and doesn't really reflect the "real" world.

Many researchers have addressed this issue before many times. Some have a specific formula that they have developed, and others use a complex mixture like baby food, dog food or milk, etc. The most important thing to do is to get enough for all your experiments and always use the same feed.

I think that research papers describing this type of research (pilot scale and modeling) should have the actual carbon substrate in the title of the paper.

Hope that this helps.