TABLE OF CONTENTS Slow rate and rapid infiltration systems are very effective for removal of suspended solids. Filtration in the soil profile is the principal removal mechanism. Overland flow systems depend on sedimentation and entrapment in the vegetative litter or on the biological slimes and are typically less efficient than SR or RI. However, OF systems can provide better than secondary effluent quality for total suspended solids (TSS) when either screened raw sewage or primary effluent is applied. Table 3.3 summarizes TSS removal at a number of land treatment systems receiving municipal wastewaters.
| Total suspended solids, mg/L | ||
|---|---|---|
| Process/location | Applied | Effluent |
| Slow Rate (SR) | ||
| Hanover, N.H. | 60 | <1 |
| Typical value | 120 | <1 |
| Rapid Infiltration (RI) | ||
| Phoenix, Ariz. | 20 100 | <1 |
| Hollister, Calif. | 274 | 10 |
| Typical value | 120 | 2 |
| Overland Flow (OF) | ||
| Ada, Okla. (raw sewage) | 160 | 8 |
| Hanover, N.H. (primary) | 59 | 7 |
| Easley, S.C. (raw sewage) | 186 | 8 |
| Utica, Miss. (facultative lagoon) | 30 | 8 |
| Davis, Calif. (facultative lagoon) | ||
| Summer | 121 | 80 |
| Fall | 86 | 24 |
| Winter | 65 | 13 |
As indicated previously,40 suspended solids removal in OF systems receiving facultative lagoon effluents is not always effective, owing to the variability of algal species present and the short detention time on the slope. The seasonal variation in performance of the Davis, Calif., system, shown in Table 3.3, clearly illustrates this problem. See Chap. 11 for additional information on this issue.
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