M. Wegelin,
“Roughing gravel filters for suspended solids removal”, in
Slow sand filtration : recent developments in water treatment technology, 1988, pp. P. 103-122: fig., tab.
L. Di Bernardo,
“Upflow coarse-grained prefilter for slow sand filtration”, in
Slow sand filtration : recent developments in water treatment technology, 1988, pp. P. 123-140: fig., tab.