Enrique J. La Motta

The effect of air-induced velocity gradient and dissolved oxygen on bioflocculation in the trickling filter/solids contact process

Abstract The trickling filter/solids contact process (TF/SC) was developed in the late 1970s to improve the final effluent quality of existing trickling filters, to be able to meet stricter effluent EPA requirements. Although the TF/SC process has been successful in achieving this goal, it is still not fully understood, and there is limited information regarding the factors affecting the flocculation phenomena occurring in the solids contact chamber (SCC), such as the effect of bubble size and dissolved oxygen on bioflocculation efficiency. To better understand the kinetics of bioflocculation in a continuous flow solids contact chamber, a long-term experimental program was conducted using a TF/SC pilot plant constructed at the Marrero, Louisiana wastewater treatment plant. This program, developed from January 1998 through October 2000, included a detailed investigation of the kinetics of the bioflocculation process taking place in the SCC. This paper deals with the effect of air-induced velocity gradient on bioflocculation. Analysis of the observed data demonstrates that excellent final effluent quality can be obtained with a wide range of air-induced velocity gradients ( G ) and with dissolved oxygen levels as low as 0.5 mg/l. However, from the point of view of SCC design, a value of G =25/s, achieved using a fine-bubble aeration system, and dissolved oxygen (DO) levels between 1.0 and 1.4 mg/l, are recommended to consistently produce a very good final effluent. This study also demonstrates that additional mechanical flocculation units would not be needed if a fine-bubble aeration system were used in the SCC and the floc structure could be preserved while transferring the floc from the SCC to the secondary sedimentation tank. However, considering that floc breakup frequently occurs during mixed liquor transfer from the SCC to the secondary clarifier, flocculator center wells should be used as a precaution in final clarification units to re-flocculate the mixed liquor.

Electro-Disinfection of Municipal Wastewater: Laboratory Scale Comparison between Direct Current and Alternating Current

Electrodisinfection of wastewater has been investigated extensively in the past, although a consensus over the use of direct current (DC) or alternating current (AC) as the most efficient electricity source has not been reached to date. The research presented herein compares the use of DC and AC in electrodisinfection of municipal wastewater aiming to provide conclusive evidence on the benefits of using one type of current over the other. During the experimental phase, a bench-scale electrodisinfection reactor equipped with iridium oxidecoated titanium electrodes was operated continuously, and E.coli inactivation, free and total chlorine generation were measured. The results observed indicate that, under the experimental conditions, DC represents a more efficient and economical alternative to electrodisinfection than AC.

Field Testing of a Small-Scale Continuous-Flow Wastewater Electrodisinfection Unit Using Direct Current

AbstractThis paper describes field testing of a small-scale, continuous-flow electrodisinfection reactor assembled with four IrO2-coated titanium plates and operated in bipolar mode using direct cu...

Discussion of “Tractive Force Design for Sanitary Sewer Self-Cleansing” by LaVere B. Merritt

In the original paper, Merritt presents a detailed summary ofChapter 5 of the 2007 edition of the joint ASCE MOP 60-WaterEnvironment Federation (WEF) FD-5 Manual, Gravity SanitarySewer Design and Construction (ASCE-WEF 2007). He endorsesthe manual’s recommendation to use the unit tractive force (TF)method to calculate the minimum slope of sanitary sewers carryingthe minimum flow at the beginning of the design period. He alsoreproduces the method to calculate such a flow, by using criteriapresented in Chapter 3 (ASCE-WPCF 1970, 1982; ASCE-WEF2007).In Merritt’s literature review, he fails to mention that the TFmethod to attain self-cleansing in sewers carrying settleableparticles was proposed as early as 1954 by Fair and Geyer,who suggested that to have self-cleansing conditions at all flowrates, the unit tractive force must be equal to that generated in asewer running full at a minimum velocity of 0:6m∕s(Fair andGeyer 1954). This minimum velocity was considered for manyyears sufficient to provide self-cleansing in a sanitary sewer run-ning full, without regard to particle size. The unit tractive force,in this case, can be calculated by using the following equation(La Motta 1996):T ¼ 0:571464γn