Procedure

LABORATORY PROCEDURE

Purpose:

The purposes of this laboratory assignment are to:

Provide an introduction to the kinetics of biological treatment.
Conduct a batch growth experiment.
Determine the rate and extent of biomass growth for a synthetic wastewater.
Demonstrate the impact of other wastewater components on biodegradation kinetics.

Introduction:

The aerobic biological wastewater treatment process utilises acclimated biosolids to oxidise soluble and colloidal organic matter under aerobic conditions to CO₂, H₂O and more cells. The activated sludge process is but one of many types of aerobic biological treatment processes where the object of the process is the conversion of dissolved and colloidal organic materials into flocculent and settleable microorganisms, non-living organic matter and inert materials. The microorganisms present and responsible for the aerobic breakdown of organic matter include bacteria, moulds, fungi, protozoa, rotifers, insect larvae and worms (Figure 1). The term activated sludge or biosolids refers to the all the metabolically active microorganisms present in the agglomerate biomass. Therefore, biosolids are complex microbial ecosystems that evolve out of the engineered environment of a biological wastewater treatment process. Conventional wastewater treatment process mathematical modelling represent this ecosystem in terms of a biosolids (biomass) term ("X"). This simplification supposes that the complex ecosystems that comprise a biological wastewater treatment process function collectively as a single pseudo-species of microorganism. Changes in the species make-up of the biomass that result from process operational or wastewater changes make for a different pseudo-species. Therefore the kinetic constants used to model the performance of biological wastewater treatment processes are not necessarily constant, since they are dependent on the pseudo-species that evolves within the treatment process.

TOP

Figure 1: Biosolids in Wastewater Treatment Systems (A Family Photo Album)

Click on any picture for a better view.

TOP

Droste provides an introductory overview of the classes of microorganisms in wastewater treatment systems (Section 6.1 to 6.3), and of the growth kinetics of microorganisms (Section 6.4). Chapter 17 in Droste discusses various aspects of aerobic biological treatment, including various process configurations and the application of mass balances involving biosolids and their growth kinetic. Sections 17.1 to 17.5 provide a good overview to the concepts (with the exception of inhibition) being applied for this fourth and final laboratory exercise for EnvE 375.

In the consideration for the engineering of any biological wastewater treatment process, determining the feasibility of a biological approach is an important first step. This determination could involve experimentation to gain preliminary expectation of the rate and extent of conversion of contaminants in the wastewater. Sometimes a wastewater may contain other contaminants that are inhibitory to biological treatment. Therefore, the preliminary assessment could also consider the potential for an inhibitory effect.

TOP

For this laboratory exercise, suppose that you are a consultant asked to consider the biological treatability of a wastewater for a client. The client needs to reduce the organic content of the wastewater. However, the client's industrial process sometimes releases silver sulphate into the wastewater. Your task is to consider the potential for impact of transient releases of the silver sulphate on the performance of biological treatment.

To do this you will conduct batch growth experiments. The batch growth experiments are conducted by inoculating a wastewater sample with acclimated biosolids and then monitoring the increase in the biomass parallel to the change in wastewater characteristics. In this case you are interested in the increase in biomass parallel to the decrease in dissolved organic matter.

Biomass in a biological treatment process can be quantified many ways. For example, changes in biomass can be inferred from changes in solids quantities (such as VSS), changes in organic quantities (such as suspended COD), and changes in turbidity (such as Optical Density). In this laboratory assignment you will be using CODs to quantify both the dissolved organic matter and biomass, and in addition you will be using optical density.

TOP

Methods and Materials

THIS LABORATORY EXERCISE WILL INVOLVE THE POTENTIAL FOR CONTACT WITH ACTIVE MICROBIAL COMMUNITIES. PERSONAL AND COMMUNAL SAFEFY AND HYGIENE MUST GOVERN YOUR CONDUCT IN THE LABORATORY.

WHILE YOU ARE IN THR LABORATORY:

EYE PROTECTION MUST BE WORN AT ALL TIMES

OPEN TOED FOOTWARE MUST NOT BE WORN

NO FOOD IS PERMITTED

WEAR PROTECTIVE GLOVES WHEN HANDLING CHEMICAL REAGENTS

WASH YOUR HANDS BEFORE LEAVING THE LABORATORY

ASK ABOUT POTENTIAL HAZARDS IN ANY PROCEDURE YOU ARE INVOLVED WITH

BE AWARE WHAT THE PEOPLE AROUND YOU ARE DOING

LOCATE SAFETY SHOWERS AND EYE WASH STATIONS BEFORE YOU DO ANYTHING

TOP

For this laboratory exercise you will form a team of four lab groups. As a team you will need to share your measurement data together. In addition kinetic growth data will be made available from the web.

Each team will be provided with four 250 mL Erlenmeyer shaker flasks and two wastewater stock solutions. One of the wastewater stock solutions will contain zero AgSO₄ and the other will contain 100 mg/L AgSO₄. These Erlenmeyer flasks will be used as the batch reactors to determine the extent of treatment and the yield of biomass. Label each flask with your chosen TEAM NAME (keep it short).

Measure the initial total COD and dissolved COD (i.e. supernatant after centrifuging) of the two stock solutions.
In each Erlenmeyer flask you will need to add 50 mL of wastewater sample. Combine the wastewater stock solutions such that you generate a flask with 0, 25, 50, and 100 mg/L of AgSO₄.
After you complete steps 1 and 2, place a foam sponge in the top of the Erlenmeyer flask and place your flasks by the shaker table.
After you leave, all the flasks will be inoculated by a 0.5 mL biosolids sample that is acclimated to the wastewater but not to AgSO₄ (See Pictures Below).

TOP

Figures 1-3. Acclimation of Biosolids to Wastewater Media.

Figure 1. Wastewater(left) and Biosolids(right) Flasks	Figure 2. Innoculation of Wastewater with Biosolids

Figure 3a & b. Innoculated Wastewater Flasks on Shaker Table

From each flask a small (200 microlitre) sample will be placed in a microplate reader well to follow the kinetics of growth (to be assumed for the shaker flasks) using optical density.

*** A PowerPoint slide show of the process by which the innoculated samples are tranferred to the microplate wells and subsequently analysed within the microplate reader can be viewed HERE. ***

TOP

In addition, calibration samples will be generated so that you can compare optical density to biomass as suspended COD.

All the flasks will be placed on the shaker table directly after inoculation. The shaker table agitates the flasks to provide continuous mixing and to also aerate the wastewater sample. Therefore, the shaking generates aerobic conditions in a completely mixed batch reactor. Similarly, the microplate reader can be thought of as a mini-shaker table that monitors optical density changes for a collection of, up to, 96 batch reactors. The microplate is also agitated to produce aerobic growth conditions.

Measure the final total COD and dissolved COD (i.e. supernatant after centrifuging) for each of your TEAM shaker flasks the following Monday Morning.

Epilogue

Within each team, each group will be responsible for exchange of their respective COD data. The microplate kinetic growth data will be downloadable off the web by the following Monday Afternoon.

Answer the questions for the associated assignment.

TOP