Laboratory and field experiments were conducted using a pilot‐scale compost biofilter (approximately 5.7 m3/min) to determine the potential of using biofiltration for removing volatile organic compounds (VOCs) from gas streams at publicly owned treatment works. Six compounds commonly found in wastewaters (benzene, trichloromethane, dichloromethane, toluene, tetrachloroethene, and trichloroethene) were selected for quantitative evaluation of removal efficiency. Gas fluxes through the biofilters ranged from 0.3 to 1.8 m3/m2·min with corresponding pressure drops of 0.1 to 0.7 kPa. Removals of aromatic VOCs averaged greater than 80% during an 8.5‐month field study and were typically greater than 90 to 95%, despite highly variable inlet concentrations. Removals of chlorinated VOCs were inconsistent and ranged from none to more than 60%. Low removals of the chlorinated compounds were believed to be due, in part, to the low inlet airstream concentrations, which were generally less than 70 ppb. Removal of H2S and odors was excellent throughout the studies, consistent with the findings of other investigators.

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A novel use of double digits in single places

ROVIDING an instructional program which is adapted to the wide range of ability levels among pupils is one of the most difficult tasks in teaching. The task is difficult in the lower grades of the elementary school, but it becomes more and more difficult as the pupils become older. Consider, for example, two pupils one of whom has an 1. Q. of 75 and the other, 125. At the age of 6, the first child has a mental age of 41/z and the second, 71/2. This means a difference of 3 years in their levels of mental growth. But at the age of 12, assuming that the I.Q.'s remain constant, the first pupil has a mental age of 9 and the second, 15. There is now a difference of 6 years in their levels of mental growth. Surely, it is more difficult to provide an instructional program suitable to pupils scattered over a 6-year range in mental development than is the case if the pupils are scattered over a 3-year range. Furthermore, the range becomes still greater beyond the age of 12. And the extremes found in a school population are frequently represented by pupils whose I. Q.'s are lower than 75 and higher than 125.The literature of education contains many discussions of the advantages and disadvantages of homogeneous grouping. Without attempting to summarize these discussions, we would merely remind the reader that in many schools homogeneous grouping is not feasible and, in others, is not possible. How can the teacher best provide for the needs of pupils representing a wide range of ability levels when those pupils are all members of one class? In the following paragraphs, an attempt will be made to provide, briefly, an answer to this question.The plan here described may be designated by the phrase, &dquo;Grouping in depth.&dquo; When the class as a whole has covered a unit of work-a unit which requires two, three, or four weeks for completion-a diagnostic test is given. The test covers all of the essential ideas in the unit. The results of this test indicate that the pupils may be classified into three groups which we may call: (1) the slower learners; (2) the average learners; and (3) those who excel. The experiences provided for the three groups are now differentiated.