Texas Waste Water Treatment #13 Application of Lab Ctrl Determinations

Laboratory tests in wastewater treatment plants are a necessary part of plant operation. They allow the operator to determine effluent quality for self-monitoring and reporting, >measure operation efficiency<, and calculate >the effect of the discharge, including the extent of pollution, on the receiving stream<. Laboratory tests also reveal problems caused by improper operation of any part of the treatment plant, discover any unusual wastes that are discharged into the wastewater stream, and find problems caused by overloading. They also help determine the effectiveness and monitor the operation of individual treatment units. On the broadest level, they >measure the strength and composition of the raw wastewater entering the plant< and evaluate any problems caused by unusual wastes dumped into the system. Once problems are discovered, the operator can make adjustments to fix the issue. Continued testing can make sure that the solution was successful and discover any new problems.

One method of sampling is to “grab” a sample of the flow, collecting and analyzing it in less than 15 minutes. Flow rate and wastewater strength change throughout the day and night. The influence of most industrial wastes also varies widely throughout the day and night depending on the time, length, and quantity of discharge. The composition of the grab sample can vary widely, depending on when it is taken, and only represents the flow at that particular time. pH, chlorine residual, and dissolved oxygen (DO) must be run on a grab sample. NOTE: yes the snippet from the book says that both pH and chlorine residual are valid answers however as previously stated the answer key and therefore the test says chlorine residual is the answer you should select.

A composite sample is a representative average sample taken by combining portions of samples taken at regular intervals throughout a definite sampling period. To represent daily operation, the period is usually 24 hours. The most common sampling schedule is once every 2 hours for 24 hours for 12-part composite, although sampling will vary according to need. If flow composition varies widely and rapidly, for example, portions of the composite samples should be taken more frequently. To prepare a flow-weighted composite sample, the flow is measured with a flow meter when the portions are collected. The hourly samples are then aliquoted in proportion to the flow rate that was recorded at the time of each sample. FORMULA: (Flow (MG) at time of sampling X Amount of sample needed (mL)) / (Number of portions X Average flow (MG)) = volume of each portion to be added to the composite sample (mL)

The BOD test, a major parameter in quality control, determines the BOD (oxygen usage) of wastewater. The BOD of raw wastewater may indicate the absence or presence of industrial wastes. It also enables the operator to determine the pounds of BOD/day that must be treated.

For anaerobic digesters the optimum pH is about 7.0. When the pH is below 6.0 or above 7.2, efficiency and quality decrease. At a pH of 8.0 there is little or no activity, and at a pH of 9.0 digestion will cease. | As the acid-forming bacteria in the digester convert the organic matter to volatile acids, these acids must be used by the methane-forming bacteria. If they are not, a low pH will result. By the time the low pH is noticed, it will be too late; the volatile acids will have already created poor conditions in the digester pH in an oxidation pond changes throughout the day. During daylight hours, algae utilize carbon dioxide and the pH rises. During the night, the process of respiration restores the carbon dioxide as algae cease photosynthetic activity and the pH is lowered. | When chlorine is added to water, it forms a mixture of hydrochloric acid (HCl) and hypochlorous acid (HOCl). Hydrochloric acid is not a disinfectant. The hypochlorous acid compound ionizes into H+ and OCl. The degree of ionization depends on the pH. (Cl2 + H2O -> HOCl (Hypochlorous) + HCl (Hydrochloric)) Hypochlorous acid is extremely effective as a disinfectant, but the hypochlorite ion (OCl) is not. At a pH of 4 or 5 the HOCl concentration is almost 100%. As the pH increases, the percent HOCl decreases, thus decreasing its disinfecting capabilities. At a pH of 7.0 the HOCl concentration is about 70%–80%

Total solids, or total residue (TR), are all the solids present in wastewater regardless of form or composition. Total solids consist of suspended and dissolved solids so neither will be "greater than the total solids". If for some reason you think suspended or dissolved solids are not in a solution i would ask you what you think they are suspended or dissolved IN while looking at you funny. Oh yeah, the book also defines suspended and volitile solids thusly: Total suspended solids (TSS) are those that can be filtered out. Volatile suspended solids (VSS) is the amount of TSS that is volatile. VSS is determined by burning the TSS sample at 550°C, which burns off all of the organics.

A chlorine residual of 1.0 mg/L after a 20-minute contact period is necessary to destroy disease-causing (pathogenic) bacteria. This contact period will not destroy all bacteria, nor will chlorine demand necessarily be satisfied; however, disease-causing bacteria will be killed.

Table 13.1 in the book lists a number of tests that, under normal conditions, help determine digester loading, >progress of digestion<, quality of digested sludge and supernatant, overall plant performance, and possible problem areas.

Table 13.1 in the book lists a number of tests that, under normal conditions, help determine >digester loading<, progress of digestion, >quality of digested sludge and supernatant<, overall plant performance, and possible problem areas.

For anaerobic digesters the optimum pH is about 7.0. When the pH is below 6.0 or above 7.2, efficiency and quality decrease. At a pH of 8.0 there is little or no activity, and at a pH of 9.0 digestion will cease.

The volatile acids concentration may best indicate the anaerobic digester condition. Volatile acids content indicates digestion progress and may forecast future problems. An increase in the volatile acids content indicates danger, while a decrease indicates an improvement. The volatile acid concentration in a well-operated anaerobic digester ranges between 50 mg/L and 300 mg/L. Values below 500 mg/L usually indicate good digestion.

Tests for the successful operation of an activated sludge plant include the following: • Dissolved oxygen (DO) • Biochemical oxygen demand (BOD) or chemical oxygen demand (COD) • Total suspended solids (TSS) • Volatile suspended solids (VSS) • >30-minute settling test (SS)< • Sludge volume index (SVI) • >Oxygen uptake rate (OUR)< • Gould sludge age (GSA) • >Microscopic examination

The SVI is the volume in milliliters occupied by one gram of activated sludge after settling for 30 minutes in a 1-liter graduated cylinder. The lower the SVI, the faster the mixed liquor settles. The higher the SVI value, the slower the mixed liquor settles. An SVI from 70 to 150 is typical for normal activated sludge. An SVI below 70 indicates that the sludge is settling so rapidly that poor clarification will result. When the SVI exceeds 150, there is a tendency for the sludge to begin bulking and solids to be sent over the weir of the final clarifier

An SVI below 70 indicates that the sludge is settling so rapidly that poor clarification will result.

The dissolved Oxygen Uptake Rate (OUR) test is a simple and valuable way to determine the condition of the activated sludge process. It is a measure of the activity of microorganisms in the system. The OUR should be measured each day on samples of mixed liquor and RAS to establish a typical OUR. This normal value should be established during times the plant is operating efficiently. Measuring the rate at which oxygen is being used in a sample and comparing the results with normal values for the plant will show whether the microorganisms are more or less active than usual. An uptake rate lower than the normal value indicates low activity and impending problems. A low OUR could be the result of a lower-than-normal BOD loading, a pH level that is too low or too high, low DO levels, or the presence of toxic materials. An uptake rate higher than the normal value indicates higher biological activity resulting from a higher influent BOD loading.

The operator is concerned with the presence and numbers of four types of microorganisms—amoeboids, flagellates, ciliates, and rotifers—and records them on a worksheet to analyze activated sludge condition. The sludge will be described by one of five conditions. Condition l. Amoeboids will be present and predominant in mixed liquor floc during start-up periods or excessively high organic loads. The sludge will not flocculate satisfactorily, and the activated sludge condition will be poor. Large numbers of flagellates may also be present under these conditions Condition 2. Shows a decrease in the number of amoeboids, about the same number of flagellates, but a marked increase in the number of free-swimming ciliates. Stalked ciliates are beginning to show up. The sludge condition has improved over Condition 1. Some flocculation is evident and conditions are improving. Condition 3. Shows a reduction in the number of flagellates. A predominance of free-swimming ciliates are present that feed on the bacteria and clarify the effluent. Good flocculation is experienced along with improved settleability. >Condition 4. Indicates a good sludge quality. The sludge settleability is good and the BOD of the effluent is low. A healthy sludge will contain all of these animals in a highly active state.< Condition 5. As the sludge gets older and highly oxidized, quality deteriorates and higher life forms, such as rotifers, become dominant. Rotifers are often the dominant form of life in extended aeration systems, especially in aerobic digesters in contact stabilization plants.