The authors review key parameters and engineering variables influencing biological filtration and identify areas requiring further research. Biological filtration, an important process step for the production of microbially safe and aesthetically pleasing drinking water, has attracted increased attention within the water industry. In many cases, the most economical way to implement biological rapid filtration is to achieve biodegradable organic matter (BOM) removal and particle removal within the same filter unit, i.e., single‐stage biological filtration. This requires optimization of the filtration process, keeping in mind both treatment goals: BOM and particle removal. This article presents a critical review of the key parameters and engineering variables influencing the biological performance, as well as the conventional performance, of biologically active filters. Several areas requiring further research have been identified.

OPTIMIZING TREATMENT PROCESSES n terest in u sin g ozon ation h as in creased in th e North Am erican water in du stry. On e con sequ en ce of th e reaction of ozon e with n atu ral organ ic m atter is th e form ation of organ ic ozon ation by-produ cts (OBPs). Organ ic com pou n ds th at h ave been iden tified as OBPs in clu de aldeh ydes, 1 oxoacids, 2 an d carboxylic acids, 3,4 alth ou gh data for th e organ ic acids are scarce. Som e aldeh ydesfor exam ple, form aldeh yde, acetaldeh yde, an d glyoxal-are kn own or su spected m u tagen s an d carcin ogen s. 5 Carboxylic acids are n ot con sidered a direct toxicological h azard; 5 h owever, organ ic acids m ay en h an ce th e growth of m icroorgan ism s in distribu tion system s or react with ch lorin e to form u n wan ted organ oh alides. 6 Th is article p re se n ts d ata o n th e fo rm atio n an d re m o val o f carbo x ylic acid s in a fu ll-scale tre atm e n t p lan t e m p lo yin g o zo n atio n an d bio lo gical filtratio n . Carbo x ylic acid co n ce n tratio n s in cre ase d afte r o zo n atio n an d d e cre ase d th ro u gh su bse qu e n t filtratio n . Sim p le lin e ar re latio n sh ip s be tw e e n m ajo r w ate r qu ality p aram e te rs (e .g., te m p e ratu re , p H) an d acid fo rm atio n d id n o t e x ist. Yie ld s o f carbo x ylic acid s o n o zo n atio n w e re an o rd e r o f m agn itu d e gre ate r th an fo r th e co rre sp o n d in g ald e h yd e . A n e m p irical lin e ar m o d e l co u ld d e scribe th e re m o val o f carbo x ylic acid s th ro u gh bio lo gical filtratio n fro m a p ractical p o in t o f vie w . Ho w e ve r, th e d ata su gge st th e re m o val m e ch an ism m ay be co m p le x . A lth o u gh co n tact tim e s in th e filte rs w e re qu ite lo n g (o n th e o rd e r o f 30 m in ), re m o val o f se ve ral carbo x ylic acid s w as in co m p le te (e .g., ave rage e fflu e n t co n ce n tratio n o f fo rm ate w as 44 µ g/ L).

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In the late 1980s, the Erb Street landfill, located in Waterloo, Ontario, Canada, had a very large leachate mound, thus a perimeter toe-drain system was installed. The leachate was sent to the Waterloo Waste Water Treatment Plant via the sewer system. This study investigated possible effects of the leachate on the treatability of the sewage with respect to oxygen demand, BODs loading, nitrification capacity, and the metal concentrations in the sewage biosolids. The quantitity of leachate produced at the landfill and its contaminant concentrations were predicted and compared with measured values. Based on the predictions, it was shown that the leachate strength would not exceed its current strength in the future. The average BOD; and ammonia loads of the leachate were estimated to represent -2% of the total loads of the sewage. Also, the leachate metal contribution to the sewage was significant.