Environmental Engineering Reference
In-Depth Information
Research is being conducted to solve the problem of using feedstock with high content of
FFAs and moisture. Alternatives vary from the use of microorganisms of the genus
Rhizopus
as biocatalysts (Jin et al., 2009) to heterogenic acid catalysis (Melero et al., 2009) and enzymes.
Many papers report the successful production of biodiesel in the laboratory using lipases;
however, the commercial use of enzymatic esterification still has the high cost of the lipases
to consider.
Yellow and brown grease can be used as fuel sources without previous transformations
into biodiesel. A demonstration conducted at the University of Georgia proves that yellow
grease (in addition to other natural fats) can be burned in a boiler as a replacement for No. 2
fuel oil with an efficiency of the 75.6 percent in contrast with 80.2 percent for No. 2 fuel oil.
Their tests demonstrated that yellow grease and the other fats tested burn cleanly, without
odor, and with no damage to the equipment (Adams et al., 2002). Another study indicates
that brown grease can be burned instead of diesel in a gas turbine generator after preheating
the grease to 80°C to reach atomization viscosities (Al-Shudeifat and Donaldson, 2010).
Moreover, brown grease could be used without modifications in systems that regularly
burn No. 4 and No. 6 fuel oil because they already are equipped with fuel preheaters
(Tyson, 2002).
Chemicals and ingredients from solid waste
A variety of solid waste materials from several
food-processing industries has potential as raw material for the recovery of chemicals and
production of ingredients. The fruit and vegetable industries—in particular canning and juice
extraction—generate leftovers that contain starches, antioxidants, color compounds, fiber, and
vitamins. The maximum recovery of useful compounds and ingredients, before sending the
waste to the next step of the Food Waste Recovery Hierarchy, supports the idea of the biorefinery
that is explained in Chapter 14.
The animal protein industry produces waste materials from which valuable biomolecules
can be extracted before sending these materials to rendering. For instance, roosters' combs
and wattles are rich in hyaluronic acid, a compound used in the cosmetic industry, and the keel
bone of young broilers contains significant amounts of chondroitin sulfate, which is employed
as a nutritional supplement (or as a drug in the European Union) to alleviate osteoarthritis
symptoms in humans and companion animals (Morawicki, 2010).
Extraction of chemicals, or ingredients, from waste products has environmental impacts
that need to be considered and evaluated. If the environmental impact produced by the
recovery process is too high, then it is wise to consider a lower impact alternative such as
composting.
Composting and biogas production
Composting
Food wastes of all types can be composted along with cellulosic materials, such
as paper and wood chips from pallets and containers. There is one exception, though, fats and
oils. They can be added in small quantities to compost piles, but it is recommended to use
alternative uses for these materials.
Composting is the controlled biological degradation of organic materials in aerobic
conditions that yields a rich matter used as soil amendment or mulch. During composting,
microorganisms break down the starting material into carbon dioxide, water, heat, and compost
(EPA, 2000). The heat generated during composting pasteurizes the compost, which eliminates
most undesirable pathogenic organisms and seeds. Ideally, the starting material must contain
carbon and nitrogen to a ratio of 25 to 35 parts of carbon for each part of nitrogen. A lower
ratio results in the emission of ammonia odors, and a higher ratio prevents the compost from
reaching high temperatures yielding lower quality compost (EPA, 2000).
