Document Type


Date of Award


Degree Name

Master of Science in Chemical Engineering - (M.S.)


Chemical Engineering

First Advisor

George C. Keeffe

Second Advisor

Saul I. Kreps

Third Advisor

C. L. Mantell


Disposal of waste, and specifically organic waste, has become a serious problem in such industries as the canning, meat-packing, dairy and other food producing industries. Recently, with the introduction of instant coffee powder, this particular industry now has a waste disposal problem with the resultant coffee residue. Composting or biologically decomposing this waste to yield an organic fertilizer is one of the many ways to solve this problem.

There are no papers in the literature concerning composting of coffee waste and only one paper (65) is available covering studies of high rate composting of garbage and refuse. It is known that work is being conducted by Wagner College and Michigan State College (46) in the decomposition of garbage on a pilot plant scale but as yet, no data has been published. Composting equipment has been patented by Earp-Thomas (13) (14), Taylor et al (77) and Eweson (21). However, none of these designs have proven to be practical on a commercial basis.

It is the purpose of this paper to study over a twelve hour period, the important composting variables associated with the aerobic, thermophilic decomposition of coffee waste. The aerobic process was selected because other composting investigators (13) (21) (46) (77) (85) advocated its use and because supposedly (31), the maximum decomposition of the organic matter is effected in the shortest possible time, process variables are easier to control and end products are odorless.

This study was successful in determining the optimum values (table XVIII) of the composting variables which are; air rate--3.6 cubic ft./lb.COD/hr., agitation--315 RPM., temperature--130?F., and the ratio of active to raw waste--2:1. Autoclaving of the raw waste almost triples the normal rate of decomposition. Under optimum conditions, disregarding waste autoclaving, the maximum reduction in oxygen demand was 7% in twelve hours and calculated to 8.5% in twenty-four hours. It is estimated that the bioxidation of coffee waste, if allowed to continue, would cease after 4 to 6 days with a maximum decomposition of 20 to 25%. This value is slightly lower than that of Wiley (85), who lists a 30% reduction in 6 to 9 days. The difference is due to; 1.) greater organic complexity of coffee waste, 2.) toxic materials such as formic acid and hydroquinone, 3.) the probable effect of coffee oil and fat coating micro-organisms and preventing them from functioning. Gurnham (27) reported that this latter condition existed in domestic garbage because of the fats and grease present.

Prior to undertaking this study, it was hoped that a 40% reduction of oxygen demand in twelve hours would be attained since it is necessary to have a final reduction of 50 to 60 percent in order to effect a satisfactory compost according to Martin & Wakeman (45). Therefore, it is concluded that the aerobic process, which gives an estimated final reduction of 2O to 25 percent for coffee waste and 30 percent for garbage, does not produce an acceptable compost for commercial use.

It is believed that satisfactory composting of organic waste can be achieved by using the anaerobic bioxidation method. This belief is supported according to recent data assembled by Gurnham (27) and the present application of this method to produce compost from brewery (56) and meatpacking (41) wastes. It is recommended that the anaerobic method be investigated in the composting of coffee waste with regard to evaluating the variables of temperature, agitation, micro-organism concentration and waste conditioning.

This is the first paper to submit a method for solving the problem of coffee waste disposal. This is the first paper to study the variables of temperature, ratio of active to raw waste and waste conditioning by autoclaving in the aerobic bioxidation of coffee waste or any solid organic waste to produce compost. This is the first paper to use a modified form of the chemical oxygen demand method as developed by Pepinsky et al (55) to determine the rate of concentrated, organic waste decomposition which satisfies the demand for a suitable unit of measure.



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