Respirometry Study about the Olive Oil Effects in the Activated Sludge Process 1
The problem of Oils in the Activated Sludge Process In many activated sludge plants excessive oils discharges can give rise to Nocardia foaming which causes major operational problems. While the bulk of the oils are removed in Dissolved Air Flotation (DAF) units or grease interceptors the remainder must be treated in the wastewater treatment system. But however, in case of high concentration, this remainder oils can create important problems on the normal operation of the activated sludge process. The plant of the study do not reach the have an important high olive mill wastewater which, besides a high organic it can contain an important amount of polyphenol. However there is an important bulk of oil in the influent, the DAF looks not to be enough efficient and the remainder oil is sufficient to create problems. In this plant, the oils presence is not only creating Nocardia foaming but also making its influence in the COD fractions, where the readily biodegradable fraction could not be actually considered as easily biodegradable. As well, in this specific activated sludge process, the low readily biodegradable COD fraction, together with its low biodegradability, is maintaining a serious repercussion in the C/N/P nutrients ratio. In this study the effects of the olive oil in the activated sludge process are analyzed by making use of the BM-T multifunction respirometer from SURCIS, S.L. (Spain) and its powerful software to obtain the different COD biodegradable fractions, overlaying Respirograms and determining the actual COD uptake rate. From the Respirometry study it was demonstrated that the presence of the Oils in the activated sludge process is seriously affecting the COD fractioning, Biodegradability and COD removal rate. 2
RESPIROMETRY SERVICE This report is based on a summary of the original report that the company SURCIS, S.L. (Spain) had made up from one Respirometry service to a real activated sludge process in a municipal wastewater treatment plant of Spain. The SURCIS personnel that have developed the present study are: Josep Xavier Sensada Emilio Serrano Instruments Respirometry System: BM-T multifunction respirometer. Thermostatic bath system Laboratory accessories. Samples and Compounds Wastewater from influent to the ASP. Activated sludge under endogenous state. Solution of Sodium Acetate. Date This Respirometry study was made on February 2008. 3
Main Features in the Activated Sludge Process (ASP) PARAMETER Process type VALUE /COMMENTS Conventional Plug-flow Nitrification process NO ph 7.3 Total COD (mg/l) in influent to ASP 404 Soluble COD (mg/l) in influent to ASP 181 BOD 5 (mg/l) in influent to ASP 245 Q: Influent flow (m 3 /h) 2915 Aeration tank volume (m 3 ) 19,125 MLSS / MLVSS (mg/l) 1950/1540 SRT: Sludge Age (d) 2 F/M (BOD) 0.38 r: Recirculation rate (%) 130 Disolved Oxygen (ppm) Aeration type 0.5 to 0.9 (end) Fine bubbles from diffuser membranes Nitrogen (mg/l) in influent to ASP 60 Phosphorous (mg/l) in influent to ASP 14 Oil (mg/l) > 120 ASP Problems The current problems in the activated sludge process of this municipal wastewater treatment plant can be summarized as it follows: Poor ASP efficiency. Nocardia foaming. Poor settleability. 4
1. Respirometry 5
1.1. COD Fractions in the ASP influent In order to establish some ranges of normality on the COD fractioning we are making use of the following table: 1.1.1. Readily biodegradable COD fraction: rbcod 0 The Respirometry test is carried out starting from a wastewater sample from influent to the activated sludge process, which was previously filtered at 0.45 micron in order to get it soluble. rbcod Respirogram 6
rbcod test results rbcod o = 61 mg/l Analysis of the result 61 mg/l of rbcod o is approximately the 15% of the total COD (COD o ). This value represents a low range of the readily biodegradable COD fraction. 1.1.2. Biodegradable COD fraction: bcod 0 The Respirometry test is carried out starting from a no-filtered wastewater sample from influent to the activated sludge process. bcod Respirogram 7
bcod test results bcod o = 312 mg/l Analysis of the result 312 mg/l of bcod o is approximately the 77% of the total COD (COD 0 ). This value represents a normal range of the biodegradable COD fraction. 1.1.3. Slowly biodegradable COD fraction: sbcod 0 sbcod o = bcod o rbcod o sbcod o = 312 61 = 251 rbcod o & bcod o overlying Respirograms 8
Analysis of the result 251 mg/l of sbcod o is approximately the 62% of the total COD (COD 0 ). This represents a relative normal range of the biodegradable COD fraction. However, since the rbcod is in the low range, from the global view of the COD fractioning, we could consider that most part of the biodegradable COD is going to the slowly biodegradable fraction. 1.1.4. Unbiodegradable COD fraction in the ASP influent: ucod 0 ucod 0 = COD o - bcod o ucod 0 = 404 312 = 92 mg/l ucod 0 = 92 mg/l Analysis of the result 92 mg/l of ucod o is approximately the 22% of the total COD (COD 0 ). This value represents a relative high range of the unbiodegradable COD fraction. 1.1.5. COD fractioning tree 1.2. Nutrients ratio Although traditionally, for municipal plants, it is stipulated an ideal nutrients BOD/N/P ratio of 100/5/1; the reality is that most part of carbonaceous material utilized by the microorganims is coming from the readily biodegradable COD fraction (rbcod). For that, although in this plant the BOD 5 value (245 mg/l) could be considered under a normal range, the rbcod value (61 mg/l) is however very low. If we rely on the data provided on total nitrogen (60 mg/l) and soluble total phosphorus (14 mg/l), the actual rbcod/n/p nutrients ratio will get the following result: DQOrb/N/P = 100/98/22 9
1.3. Biodegradability The percentage of the total biodegradable fraction in the total COD is not enough to characterize the biodegradable profile of the wastewater. The reason lies on the fact that the readily biodegradable fraction represents an important factor that is very much decisive on the stability of the activated sludge and its bioactivity; and this should be very much taken into account at the time to assess wastewater biodegradability referred to the activated sludge bioactivity. For the above reason, in this study, by separate we analyze the ratio of the total biodegradable and readily biodegradable fractions with the total COD entering in the activated sludge process. 1.3.1. bcod o Biodegradability bcod o /COD o = 312 / 404 = 0.77 In percentage, it represents a biodegradability of 77% Analysis of the result We analyze the result in base of the following table: bcod o % Biodegradability Type > 85 Very biodegradable 70-85 Medium biodegradable 30-70 Low biodegradable < 30 Non-biodegradable bcod o /COD o represents a 77% of biodegradability, and it can be classified as medium biodegradable. 1.3.2. rbcod o Biodegradability bcod o /COD o = 61 / 404 = 0.15 In percentage, it represents a biodegradability of 15% Analysis of the result We analyze the result in base of the following table: rbcod o % Biodegradability Type > 30 Very biodegradable 20-30 Medium biodegradable 5-20 Low biodegradable < 5 Non-biodegradable rbcod o /COD o represents a 15% of biodegradability, and it can be classified as low biodegradable. 10
1.3.3. Comparison of the bcod o versus rbcod o biodegradability Although it seems the global biodegradability coming from bcod o /COD o is normal, when we go to the rbcod o /COD o we realize that it is very little. Because the readily fraction is decisive for the activated sludge process performance, we have to say that the biodegradability is low and within relative terms we can say that it is due to the fact that most part of the total biodegradable fraction is slowly biodegradable. This is the first direct effect of the oils presence in the wastewater entering in biological treatment process. Another thing to take in consideration is that the high unbiodegradable fraction together with the relative high slowly biodegradable fraction represents the 85% of the total COD. 1.4. Actual COD uptake rate (q H ) When the biodegradability is referred to a specific activated sludge process it should include an analysis about how fast the wastewater readily biodegradable COD fraction is being removed. For this analysis we compare the maximum specific rbcod uptake rate of one determined standard with the actual wastewater rbcod uptake rate. The objective of this analysis is to know if the oil presence in the wastewater is able to reduce the sludge activity within the specific rbcod uptake rate. In general from the BM-T respirometer tests we calculate q H as follows: q Hmax = bcod * 24 / (VSS * t) 1.4.1. Actual COD uptake rate from one standard reference (q H,Ac ) As standard reference we have selected a solution of sodium acetate, which is very readily biodegradable and commonly accepted as a Respirometry reference. The test is carried out by means a dynamic Respirometry mode by adding a determined volume of the solution into the activated sludge. By making use of the exclusive software applied to the corresponding Respirogram, it was automatically calculated the amount of COD removed. 11
bcod Respirogram for S. Acetate COD removal q H,ac.max = 0.19 (mg/mgvss.d) 1.4.2. Actual COD uptake rate from influent wastewater (q H,S ) bcod Respirogram for Wastewater COD removal q H,S = 0,11 (mg/mgvss.d) 12
Analysis of the results The value of the COD uptake rate in the acetate is more that 60% of the one coming from wastewater. That means it should be a component in the wastewater responsible to create an important bioactivity decrease in the heterotrophic biomass. The Respirometry is demonstrating that although the test was carried out with a soluble sample the theoretical readily biodegradable fraction in fact is not so much readily; and the explanation of this abnormal feature may come from the oils presence together with the poor nutrients ratio. 1.4.2.1. Analysis of the COD uptake rate from sodium acetate (q H,Ac ) related with F/M [rbcod] One of the ways to assess the value of the COD uptake rate from wastewater is to compare it with the F/M (rbcod) First of all, we have to calculate the value of the F/M [rbcod] F/M [rbcod] = Q o * rbcod * 24 / (VSS * V) We take the values from the ASP features: F/M [rbcod] = 2,915* 61 * 24 / (1,540 * 19,125) = 0.14 The thumb rule is that, for a normal activity, the actual q H,S should be higher than F/M (rbcod) Then, if we compare both results: q H,Ac (0.19) > F/M [rbcod] (14) Analysis of the result The q H,Ac is higher than F/M [rbcod]. It means that, the removal rate on the acetate is normal and the bioactivity of the sludge is on the appropriate range. This test has another indirect important meaning: There is not toxicity in the endogenous sludge. In other words: in case low bioactivity, it would be created from an external source when reacting with the sludge, but not from the own pure sludge. 13
1.4.2.2. Analysis of the COD uptake rate from wastewater (q H,S ) related with F/M (rbcod) Here we also assess the value of the COD uptake rate from wastewater in order to be compared with the F/M (rbcod) From the previous point: F/M [rbcod] = 0.14 Fr a normal activity, te actual q H,Ac should be higher than F/M [rbcod] Then, if we compare both results: 0.11 (q H,S ) < F/M [rbcod] (0.14) Analysis of the result The q H,S is lower than F/M [rbcod]. It means that, even the value of the rbcod (61) is relatively low, due to the low removal rate that it is acquiring in the actual activated sludge process; it may be an overloading problem. By other side, in this analysis it is also demonstrated that the behaviour of the readily biodegradable COD is not taken enough features to be considered as readily biodegradable substrate. 14
2. Coclusions 15
2.1. Conclusions The conclusions are presented on a table divided in three columns in order to better understand the consequences and effects provoked by the oil presence. Points State Effects Conclusions 1.1 1.1.2. Although the bcod % and sbcod % it could be considered as normal; when compared with the small rbcod % value, it could be considered that sbcod is the most part of the biodegradable COD in the ASP. No direct effects Possible poor ASP efficiency. 1.1.4. The unbiodegradable COD is too high. Together with the non-removed sbcod, it could provoke a COD in effluent out of the low. 1.3. 1.3.2. 1.3.3. The % Biodegradability of the rbcod within the total COD is low. Poor carbonaceous organic. 1.4. The rbcod uptake rate is too low. Could be not considered as pure readily biodegradable. Poor carbonaceous nutrient. Poor ASP efficiency. Low bioactivity. Low bioactivity Possible overloadings in the ASP. 1.4. 1.4.2.1. The rbcod uptake rate from the reference of sodium acetate is higher than F/M [rbcod] Current F/M is not adapted to the actual ASP state. Low bioactivity Possible overloadings in the ASP. 1.4. 1.4.2.2. The rbcod uptake rate from wastewater is lower than F/M [rbcod] There is a biomass activity reduction with wastewater but not with a reference compound. The pure biomass is not affected by toxicity, but the bioactivity decrease when wastewater reacts with it. ASP Features Fine bubbles in aeration system. To jointly act with the rest of consequences. Bulking and Nocardia foaming. 16
3. Recommended Solutions 17
3.1. Possible solutions to the problems derived from oil presence in ASP In view of the results of the study, SURCIS has proposed some general solutions oriented to start solving the current problems. Cut or reduce the oil discharges in the ASP by improving the DAF performance. Adapt the aeration system to the actual situation. Correct the operative parameters. Bioaugmentation treatment by specific micro-organisms specially designed to degrade vegetable oils (e.g. BFL 5050VF from Biofuture Contact Surcis) Respirometry study continuation for any change in ASP Bibliography Surcis BM-T applications manual - Bioresour Technol. 2007 - Y F Tsang, S N Sin, H Chua - Mountain Empire Community Collage Wastewater Distance Learning Course. 2007 - Problemas biológicos por microorganismos filamentosos - Control of Activated Sludge Bulking and Foaming, Second Edition, D. Jenkins, M.G. Richard and G. Daigger, Lewis Publishers, Boca Raton, FL, 1993. - Jenkins et al. (1993; 2003) Emilio Serrano SURCIS, S.L. Encarnación, 125-08024 Barcelona (Spain) Tel. +34-932 194 595 E-mail: surcis@surcis.com Web. www.surcis.com 18