Browsing by Author "Weeks, R. Kenneth"

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    Iron recovery from a representative water treatment plant sludge
    Weeks, R. Kenneth (Virginia Tech, 1974)
    Water treatment plant sludge disposal has become a timely problem to consider. While many methods of sludge treatment and disposal have been suggested, coagulant recovery may prove to be the most economical. This investigation was concerned with recovery of iron coagulant by chemical addition. Sulfuric acid, hydrochloric acid, and sodium hydroxide were added to a water treatment plant sludge containing precipitated iron. The acidic method of recovery proved to be technically feasible. Iron dissolved upon addition of acid to the sludge. The concentration of soluble iron increased substantially when the pH was lowered to a level of 2.0 and then diminished at pH values below 1.0. Iron recovery appeared to generally follow the stoichiometry predicted. Acid addition to the sludge resulted in an improvement in sludge dewatering properties. Settling rates increased consistently with greater amounts of acid added, causing substantial reductions in sludge volume. The filterability of the sludge was also improved. Specific resistance decreased as the pH was lowered, reaching a minimum value at a pH level of about 3.0, and then increased due to compaction. Sludge volume reduction and iron recovery did not occur simultaneously at a given pH. It appeared that the acid acted to either solubilize the iron or to destabilize the colloidal particles, depending on the system pH. The recovered iron proved to be superior to fresh iron for coagulation of low turbidity waters. The suspended solids in the recovered iron solutions appeared to aid in nucleation. While coagulation with fresh iron resulted in a lower raw water residual turbidity, the critical coagulation concentration was less when recovered coagulant was used.
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    Recovery and reuse of coagulants from treatment of water and wastewater
    King, Paul H.; Chen, Ben Hsueh Hai; Weeks, R. Kenneth (Water Resources Research Center, Virginia Polytechnic Institute and State University, 1975)
    The focus of water quality research in the decade ahead will emphasize the development of processes which will enable reclamation and reuse as opposed to wastewater treatment and disposal to a nearby water course. In th is regard the importance of chemical treatment processes similar to those utilized by the water utility industry for many years is now well established. Two problems in this type of system are the increasing expense and scarcity of appropriate chemicals and the resulting large volumes of sludge. The use of coagulant recovery techniques promise~ to alleviate both problems. Until economical coagulant recovery schemes have been developed, the potential benefits associated with water reuse cannot be fully realized. The primary objectives of this research were to evaluate the possibilities and procedures for coagulant recovery in chemical treatment processes employed in water and wastewater treatment systems. Attention was focused on the extent of coagulant recovery achievable; the separation, dewatering, and ultimate disposal of the remaining solids after recovery; the effectiveness of the recovered coagulant during reuse; and the economic considerations which determine the feasibility of utilizing the proposed processes.