letters Methane from a n i m a l wastes
DEARSIR: The letter from D r , Hinrich Bohn in your July issue ( p 5 7 3 ) suggests that the vast tonnages of animal wastes he fermented to methane, thus reducing the mass by more than half and producing up to half our current need for methane. There are two hidden costs in this proposal which must be considered. The first concerns the poor quality of the gas, which is very obvious to anyone who has tried to use it in the laboratory. Digester gas contains 25% C 0 2 derived from methane fermentation as well as H,S which causes severe corrosion problems. The other cost is that of treatment and disposal of the waste supernatant liquor from the fermenter or digester. Digestion proceeds best in well mixed slurries which cannot contain much less than 20 lb of water per lb of solids and still be mixed economically. When digestion is complete, the supernatant water is highly polluted with solubilized and dispersed organic matter. Treatment of the supernatant “soup” is expensive in terms of gallons treated, even if it represents only a small part of the load on a biological treatment plant. Applying the industrial effluent charges of Chicago to the supernatant from an average anaerobic digester, I have calculated a charge of approximately $66.50 for treating the soup from the digestion of sludge from 100 million gallons of sewage. The total volume of soup is only 0.5 million gallons but the charges are based on flows of several hundred million gpd and appear to be Ion the low side. In terms of methane produced, the cost of soup disposal is approximately one half the market value on a 100% methane basis. Costs of purification and distribution are not included. In a small dedicated plant, the costs of soup treatment would be more than twice as high as at Chicago because of the poor scale factor. Other costs associated with sludge disposal would combine to make fermentation of animal wastes quite unattractive. Robert B. Dean EniYronrncntai Protection Agency Cincinnati. Ohio 45268
pollution measurements Increasing requirements for the control of pollution demand accurate and reliable field measurements of contaminant concentration on a full time as well as a Deriodic or sDot check basis. Beckman can provide many types of field conductivity instruments for both occasional measurement and continuous recording. The instruments shown are all battery operated, minimal current drain units and are specifically recommended for chemical pollution studies, salinity surveys, and similar applications prior to and in conjunction with the establishment of pollution control procedures. low cost, very light weight cotlductivity bridge. 2.5-40,OOO micromhos/cm in four overlapping ranges with a single eonductivity cell. Zero center null meter. Accuracy, 2 2 % of reading. available in a wide selection of calibrations and ranges for measurements from fresh through sea water. Manual temperature compensation standard with qutomatic compensation available as option: Zero center null meter. Accuracy 2 2 % of the reading. wide range, highly accurate. Digital readout to within %% of the reading. 1 ohm to 1.1 m e g ohms and 0.1 to 110,000 micromhos i n six overlapping ranges. rapid 3-place readout of temperature and salinity; ranges O-4O0C, and 0-40 o/oo/S. Electrodeless induction type cell. Contained in waterproof stainless steel case. Accuracy 20.3 O/OO Salinity, 20.5”C temperature. choice of chart drives. Many calibrations in micromhos/cm and O/OO salinity. Operates one month unattended.
A
measures and records electrolytic conductivity for up to one year unattended. Automatic temperature compensation standard. Punches four-place decimal values for resolution exceeding that of 11” strip chart recorder, INSTRUMENTS. INC. CEDAR PROVE OPERATIOMS 89 COMMERCE ROAD CEDAR GROVE NEW JERSEY 07W9 12011 23162W TWX 7109945781 INTERNATIONAL SUBSIDIARIES Amsterdam Capelown Geneva Glenrothsa Scotland London Mexico Cily Munich Paris Stockholm Tokyo Vienna HELPING SCIENCE AND INDUSTRY IMPROVE THE QUALITY OF LIFE
The above Beckman equipment provide accurate measurement of electrolytic conductivity derived from dissociation of dissolved electrolytes including common sea salt, acids, bases, industrial chemical salts, and such industrial gasses as HF, CO,, NH,, and SO,. In most cases an off-the-shelf model will economically solve your problem of measurement.
(Conrinllec! on page 1070) C i r c l e No. 14 on Readers’ Service Card
Volume 5, Number 11, November 1971
1069
