Speedy Mlss Development From Cow Dung, Wastewater Treatment and Sludge Recovery From the Activated Sludge Process (a-b Process) of a Paper Mill That Use Waste Paper as Raw Material - A Case Study

doi:10.21203/rs.3.rs-3006713/v1

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Speedy Mlss Development From Cow Dung, Wastewater Treatment and Sludge Recovery From the Activated Sludge Process (a-b Process) of a Paper Mill That Use Waste Paper as Raw Material - A Case Study

https://doi.org/10.21203/rs.3.rs-3006713/v1

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In this case study, process startup and operation of the Effluent Treatment plant of a paper mill that converts waste paper to paper and paper boards were investigated for 120 days. To meet water requirements for a revised production target of 100 t/d, apart from recycling 1000 m³/d of wastewater after DAF process, required additional facilities to provide secondary treatment for another 1000 m³/d of wastewater in ASP (A-B process) were provided. A new ASP (A) with an AT of 900 m³ was arranged to work in line with the existing ASP (B) of 1200 m³ capacity. Initiating culture development, 19.6 tons of fresh cow dung (seed) was added to AT of unit B containing 600 m³ of fresh ground water and the tank content was aerated. N, P, micronutrients and protein were added to AT every day. Good flocs were observed on 9th day of operation. MLSS of 1500 mg/l and a sludge volume 50 ml/l was observed on 27th day of aeration. Addition of appropriate nutrients and protein are believed to have aided sludge development and floc formation. During secondary startup, wastewater addition started (108 m³/d) on a regular basis on 27th day and was increased stepwise to 388 m³/d in 7 days and was continued till the end of this phase of the study. During 33 days of secondary startup influent BOD was in the range of 1170–1500 mg/l, organic loading ranged from 0.13 to 0.46 kg BOD/m³.d and F/M ratio ranged between 0.07 to 0.17 kg BOD/kg MLSS/d. BOD/N/P ratio of 200/5/1.5 was maintained along with addition of micronutrients and protein. On 60th day, MLSS was 6050 mg/l indicating that culture developed from cow dung got acclimatized easily to paper mill waste mostly containing cellulose. Initiating the next phase, required quantity of sludge was transferred from B to A to get an MLSS of 2800 mg/l in A and of 4200 mg/l in B. The wastewater flow of 388 m³/d, then flowing to B, was made to flow in the A-B process by providing stepwise increase to A, correspondingly reducing direct flow to B in 43 days. On 104th day, the MLSS rose to 11400 mg/l in A. During these 43 days of operation, unit A stabilized a total BOD of 6870 kg, and the volatile content of the sludge yielded was 4644 kg resulting in a yield coefficient, Y of 0.68. Organic loading ranged from 0.35 to 1.09 kgCOD/m³.d and F/M ranged between 0.04 to 0.12 kg COD/kg MLSS.d. Effluent COD ranged from 500 − 63 mg/l for an average inlet COD of 1940 mg/l. There after MLSS in A was reduced to 3600 mg/l in 4 days by harvesting sludge and the same was recycled to the pulping section of the mill. Flow was increased to 488 m³/d stepwise and the MLSS increased to 7800 mg/l in next 12 days in A. Effluent COD of A ranged from 550 − 258 mg/l and COD of the final effluent, that is, of unit B ranged from 98–105 mg/l. The production seized in the paper mill due to Covid 19 and hence this study was terminated at this stage.

DAF

ASP

A-B Process

MLSS

SVI

F/M

Paper Industry, one of the important industrial sector of any developing country, mainly relies on forest based raw material like bamboo, wood, etc. Thanks to the present-day environmental consciousness, large scale use of non-wood pulp based raw material came into existence, since the availability of raw material from forest has dwindled. In this case study, the paper mill uses recycled cellulose fibre as their raw material for the manufacturing of Kraft paper. Kraft paper is the leading paper type used for wrapping heavy bundles after corrugation. It is used in many types of packaging and is an important packaging material. Kraft papers or brown papers are strong and flexible (entrepreneurindia.co). The manufacturing of kraft paper consumes large amount of fresh water and hence is a major source of wastewater. The wastewater from the Kraft paper mill contains variety of organic and inorganic contaminants. The wastewater has high COD, TSS and TDS. The treated wastewater can be recycled for reuse in the pulp and paper industry, if the required quality could be achieved, or it can be released to the environment if its quality meets the environmental standards (Omid Ashraf, Laleh Yerushalami & Fariborz Haghighat 2015). The treatment of wastewater can either be done using physico-chemical process which produces large quantity of sludge thereby causing, disposal a further issue, or be done using biological process which results in the ultimate treatment by converting organic matter to CO₂ (Rao & Dhatta 1979). The wastewater is considered to be amenable for biological treatment without acclimatization, if the COD/BOD ratio is 0.6 or above. Many paper industries go for Activated Sludge Process (ASP) after possible cellulose recovery (DAF) and physico-chemical process (Metcalf and Eddy 2004). If the COD/BOD ratio is between 0.3 and 0.6, the wastewater needs acclimatization for biological treatment. If the COD/BOD ratio is less than 0.3, other methods are suggested for treatment (Rao & Dhatta 1979). In the case studied, the Kraft paper mill was using biological process for the wastewater treatment but the COD/BOD ratio was found to be mostly below 0.3 in analysis done many times previously in this paper mill. Moreover, the wastewater from the Kraft paper mill is known to be deficient in nutrients and micronutrients as raw material (waste paper) mainly contain only cellulose. The main challenge in employing ASP in this case study was the development of active biological sludge acclimatized to the cellulose waste. Secondly, the fluctuations in characteristics of wastewater affects the biological sludge microstructure caused by the development of filamentous organisms and non-flocculating organisms leading to poor settleability of sludge, thereby resulting in poor quality effluent. These issues are believed to be solved to a greater extent by employing A-B Process (Gray 1990) for such types of wastewaters.

Figure 1 shows the A-B Process. The process comprises two ASP units in series. A-Stage can receive high BOD loading (3–6 kg BOD/kg MLSS/d) and B-Stage receives normal BOD loading (0.15–0.3 kg BOD/kg MLSS/d). Effluent after preliminary treatment is first treated in A-stage. A-stage effluent is further treated in B-stage. A-stage effectively buffers the B-stage from variations in flow rate and influent quality parameters. This makes B-stage very stable, resulting in excellent quality effluent (Gray, 1990). This A-B process is employed in the present study.

In order to provide biological treatment for 1000 m³/d of the kraft paper mill effluent, the paper mill had provided an additional ASP unit (Unit A) consisting of an AT of volume 900 m³ and an SST of required size. This unit, A, was desired to operate in series with then existing unit (Unit B), thus implementing a two stage Activated Sludge System (A-B Process). The main objectives of this case study were to:

Develop active biological aerobic sludge using cow dung as seed.
Develop sufficient quantity of biological sludge acclimatized to specific wastewater emanating from the paper mill to be used in both aeration tanks of the A-B Process.
Operate the A-B Process using the sludge developed.
Evaluate Sludge production (MLSS), reduction in COD and BOD, sludge yield.

CSON PAPER MILLS PVT. LTD is a craft paper mill with an earlier production capacity of 50 tons/d. They use wastepaper, ie., recycled cellulose fiber (RCF) as raw material. The paper mill had an efficiently working ASP provided after Dissolved Air Flotation (DAF) process. They desired to increase the production capacity from 50 tons/d to 100 tons/d, in which case, additional wastewater generation had to be expected. In order to take care of this wastewater, an additional ASP, with an AT volume of 900 m³ was provided and was desired to be operated as Unit A, while the existing ASP having AT volume of 1200 m³ was desired to be operated as Unit B. The above two units were designed to be operated in A-B mode where the wastewater shall be first treated in Unit A, and its effluent shall be further treated in Unit B. This case study reports some operational details of the process for a period of 120 days and the details of performance evaluated during these days of operation.

5.1 MATERIALS

5.1.1 Additional ASP, Unit A, with an aeration tank of size 25 m x 8 m x 4.5 m (volume, 900 m³) and a clarifier of 8 m diameter with 3.5 m depth was constructed. (Designed as per Arceivala 2003 and Metcalf and Eddy 2004).

5.1.2 Aerobic culture development was done in the AT of Unit B. The seed used for sludge development in the aeration tank was fresh cow dung with dry content varying from 18 to 20%. A total of 19.6 tons of cow dung was added.

5.1.3 Nutrients supplied during the primary startup process (culture development) were urea, factom phos, a baby food, groundnut cake. Urea contained 46% of Nitrogen (as per manufactures) and factom phos contained 20% of nitrogen and 20% of phosphorus (as per manufactures). Baby Food, given to supply other nutrients contained 15.5 g protein, 9 g fat, 68.9 g carbohydrates, 3.8 g sugar, 0.06 g sodium, 1.4 g total nitrogen, 1.5 g linoleate, 0.54 g total phosphrous (Adapted from manufacturs and Grasius 1996) per 100 g. Groundnut cake contained 45–60% protein, 22–30% carbohydrate, 3.8–7.5% crude fibre, 4–6% minerals.

5.1.4 Wheat flour was used to supplement organic matter (COD) during the culture development. In 1g/l solution of wheat flour was found to have a COD of 1180 mg/l.

5.1.5 Buffering was done by addition of soda ash (Na2CO3) and the culture pH was maintained in the range of 7.6–7.8 in the AT.

5.2 METHODS

5.2.1 Different phases of reactor operation

Figure 2 shows the different phases of reactor operations during 120 days of study. The study was conducted in 4 phases of different durations conducted with specific objectives. These phases are briefly presented in Fig. 2.

5.2.1.1 Phase 1, from 0 to 27th day of operation (primary startup): The aim of this phase was to develop active aerobic sludge from a culture seed material rich in cellulose. Here, cow dung was used for the purpose. On the starting day, AT of B with 1200 m³ liquid volume was filled with 600 m³ of fresh water and cow dung was added in slurry form after filtering out long pieces of straw or grass. By the 3rd day of operation, cow dung added was 7 tons. Addition of baby food and groundnut cake at the rate 300 g and 1 kg respectively per 12-hour shift was started on the same day. By 4th day, the total cow dung added was 14.76 tons, addition of baby food and groundnut cake was increased to 450 g and 2 kg respectively on the day and the same was continued till the end. Addition of urea and factom phos was started on 7th day and continued till the end of the study. Wheat flour also was started from 7th day onwards as an organic source rich in fibre. Cow dung addition was resumed on 14th day and by 16th day, the total cow dung added was 19.61 tons. Hereafter no cow dung was added. Addition of groundnut cake and wheat flour was increased from 20th day to 3 kg and 4 kg respectively. Wastewater addition was done on 23rd, 25th, 26th and 27th and the total quantities applied on each day are shown in Table. 1. During these days of Primary startup, the sludge volume (SV) of AT and Mixed Liquor Suspended Solids (MLSS) of AT were determined from 7th day and 10th day onwards respectively.

5.2.1.2 Phase 2, from 27th to 60th day of operation (secondary startup): With the intention of developing sufficient quantity of acclimatized aerobic sludge that can be used in the aeration tanks of unit A and B, the wastewater flow rate was increased from 108 m³/d stepwise. A regular pattern in flow increase could not be maintained because of the non-availability of wastewater from the production side as and when desired. But it was increased stepwise depending on its availability. A flow rate of 108 m³/d was to be continued up to 32nd day, up on which it was increased to 222 m³/d and was continued up to 34th day. The increase to 388 m³/d was given on 34th day and any further increase could not be given due to shortage of wastewater. In this phase of study, urea and factom phos were added to maintain a BOD/N/P ratio of 200/5/1.5. Baby food and Groundnut cake were added as given in Table. 2 to ensure micronutrients required for the bacterial growth. No wheat flour was added during this phase. During these 33 days, SV, MLSS of the AT and COD of AT inlet were done every day. The BOD of inlet was done once in six days. The floc was measured using rectangular V-notch.

5.2.1.3 Phase 3, from 60th to 104th day of operation (putting A-B process into operation): On 60th day of operation, the MLSS of the AT was found to be 6050 mg/l. Initiating this phase of operation, required quantity of sludge from the recirculation line of B was transferred to AT of A on 60th and 61st day to result in an MLSS of 2800 mg/l in AT of A and 4200 mg/l in AT of B. On 61st day, 132 m³/d raw wastewater, that is, about 1/3rd of the total flow of 388 m³/d was given to A and the remaining 256 m³/d of wastewater to B. Additionally, B was fed with the effluent of A, thus A receiving a total flow of 388 m³/d. Feed to A was increased by 50 m³/d at 7 days interval and balance of 388 m³/d being fed to B. On 96th day the entire flow of 388 m³/d was received by unit A and its outlet to B, thus achieving the flow pattern of A-B process. This flow pattern was continued for the next 8 days, that is till 104th day. All through this phase, a BOD/N/P ratio of 200/5/1.5 was maintained by addition of urea and factom phos. Baby food was added at the rate of 2 g/kg BODin and groundnut cake at the rate of 150 g per 100 kg BODin also was added.

5.2.1.4 Phase 4, from 104th to 120th day of operation (sludge harvesting and flow increment): From 104th to 108th day, sludge was harvested from unit A by diverting the sludge recirculation line to the pulping section of the mill. During the subsequent 12 days of operation, flow was increased from 388 m³/d to 488 m³/d. Maintenance of BOD/N/P ratio, feeding of Baby food and Groundnut cake were done as in case of Phase 3. During the last 60 days of reactor operation, the flow to section A and B were measured using rectangular V-notch. MLSS of both aeration tanks, influent COD and effluent COD of both clarifier of A and of B were measured every day.

5.2.2 Analytical Techniques

The suspended solids of the AT content, named as, Mixed Liquor Suspended Solids (MLSS), the settleable solids in AT content, named as, Sludge Volume (SV), Chemical Oxygen Demand (COD) and Biochemical Oxygen Demand (BOD), pH of samples were determined as per the methods outlined in Standard Methods (2005)

6.1 Operations for 27 days

Startup schedule, nutrient addition and some salient observations are outlined in Table. 1. As the wastewater of the Paper mill mostly contains cellulose and as cow dung is known to provide good cellulose rich environment, cow dung was used as a seed material. Cow dung addition started on the 1st day and by 4th day of operation 14.76 tons of cow dung was added. Addition of baby food and groundnut cake were started on the 3rd day. Nutrients such as urea and factom phos were started on 7th day and continued till the end of the study. Wheat flour was added to supply organic matter (COD) from 7th day onwards. On 9th day, good flocs were observed. MLSS of 800 mg/l and 40 ml sludge volume were observed on 10th day. Addition of nutrients like Nitrogen (N), Phosphorus (P) along with micronutrients through baby food seems to have accelerated microbial growth and floc formation. Cow dung addition resumed on 14th day as no appreciable increase in MLSS was observed from 10th to 13th day and by 16th day, 19.61 tons of cow dung was added. Gradual increase in MLSS was observed from 15th day and on 21st day, MLSS was found to be 1350 mg/l. This increase in MLSS observed could be due to the presence of undigested cow dung solids. On 27th day, MLSS was 1500 mg/l and sludge observed to be of good settleability (sludge volume- 50 ml and sludge volume index (SVI) – 33.3 ml/g). From records of the company, it was found that this level of MLSS was obtained only after 45 days of operation earlier. An early sludge development, as seen in this study, may be mainly due to the supplementation of micronutrients and protein through baby food and groundnut cake. As good flocs were observed on 9th day, and with an MLSS of 800 mg/l on 10th day, wastewater feeding could have been started at this stage. This might have resulted in an MLSS of 1500 mg/l, still at an early stage. However, as the production has not started on a regular basis in the company, wastewater was not available. It is also felt that a second phase addition of 4.85 tons of cow dung done from 14th to 16th day could have been avoided. During 13 days of operation from 10th day, the MLSS increased from 800 mg/l to 1100 mg/l. During 3 days of further operation from 23rd, 125.5 m³ wastewater was added and by the end, that is on 27th day, the MLSS was found to be 1500 mg/l. From this study it may be concluded that on addition of 25 kg (dry weight) of fresh cow dung per m³ of fresh ground water as seed and on aeration of the medium with addition of N, P and other micronutrients, aerobic microbial flocs of good settleability shall be developed within 10 days of operation. Also, that once an MLSS of 1000 mg/l is observed in AT, wastewater loading can be started slowly.

Table 1

Startup schedule and salient observations
DAYS OF OPERATION	SEED/NUTRIENT	MLSS/SV/OBSERVATION	WASTEWATER FLOW
0	Cow dung addition started	600 m³ fresh water in AT, B	0
4	Cow dung added – 14.76 tons (cumulative) BF/GC 450g/2kg per 12 hr shift	No flocs observed in the liquid zone. Sludge zone was mostly cow dung debris	0
7	U/FP/BF/GC/WF– 250/250/450/2kg/1kg	SV-50 ml – no flocs found; sludge contained mostly cow dung debris	0
9	U/FP/BF/GC/WF– 250/250/450/2kg/1kg	Good flocs observed in the liquid zone	0
10	U/FP/BF/GC/WF– 250/250/450/2kg/1kg	MLSS-800 mg/l SV-40 ml Good flocs observed	0
13	U/FP/BF/GC/WF– 250/250/450/2kg/1kg	MLSS-900 mg/l SV-40 ml Good flocs	0
15	Cow dung added-17.18 tons (Cumulative)	MLSS-1000 mg/l SV-50 ml	0
16	Cow dung added-19.61 tons (Cumulative)	MLSS-1200 mg/l SV-50 ml	0
21	U/FP/BF/GC/WF– 250/250/450/3kg/4kg	MLSS-1350 mg/l SV-50 ml	0
23	U/FP/BF/GC/WF– 250/250/450/3kg/4kg	MLSS-1100 mg/l SV-40 ml	A total of 20.5 m³ in the day
25	U/FP/BF/GC/WF– 250/250/450/3kg/4kg	MLSS-1300 mg/l SV-50 ml	A total of 40 m³ in the day
26	U/FP/BF/GC/WF– 250/250/450/3kg/4kg	MLSS-1400 mg/l SV-50 ml	A total of 65 m³ in the day
27	U/FP/BF/GC/WF– 250/250/450/3kg/4kg	MLSS-1500 mg/l SV-50 ml	A total of 108 m³ in the day
U – urea; FP – Factom phos; BF – Baby food; GC – Groundnut cake; WF – Wheat flour; SV – Sludge volume; MLSS – Mixed Liquor Suspended Solids

6.2 Reactor operations from 27th – 60th day (secondary startup) and reactor performances

Table. 2 gives the details of stepwise changes made on specific days on parameter like wastewater flow rate to the AT, its organic strength in terms of BOD, the resulting MLSS concentration in AT, the applied organic loading based on reactor volume and organic loading based on MLSS concentration (F/M ratio). The wastewater flow rate was increased stepwise on specific days. This increase was not on a regular basis but was depending on the wastewater availability. The wastewater BOD on these days ranged from 1170 mg/l 1500 mg/l. The resulting volumetric organic loading corresponding to the provided flow rate ranged from 0.13 kg BOD/m³/d to 0.46 kg BOD/m³/d. The MLSS increased from 1500 mg/l to 6050 mg/l. It shall be noted that in 21 days of operation in this phase from 27th to 48th day, the increase in sludge concentration was 2200 mg/l whereas during the subsequent 12 days of operation, from 48th to 60th day, the sludge concentration increase was 2350 mg/l. During the later 14 days of this 21 days and till the end of this phase of study, the volumetric loading was in the range of 0.38 to 0.46 kg BOD/m³/d. This shows a slower bacterial growth at the initial stage in spite of a relatively high organic loading and a higher rate at the second stage. This is indicative of the usually observed ‘lag phase’ in bacterial growth (Monod 1949) explained to be due to the delay in adaptation to the new substrate, here the cellulose, and maximum rate of metabolic activity such a lag in growth can be seen in Fig. 3. The increased sludge production during the last 12 days in this phase and a final MLSS value of 6050 mg/l after 33 days of operation of secondary startup initially starting from 1500 mg/l indicated that the culture developed from cow dung got easily acclimatized to paper mill wastewater mostly containing cellulose. The acclimatization time required may be concluded to be around 20 days in the field condition of this study.

An F/M ratio of 0.1 kg BOD/kg MLSS/d or less, from 48th day were due to higher MLSS concentration. Lower F/M ratio results in production of exocellular enzymes by bacterial cells resulting in better floc formation (Gray 1990).

Table 2

Hydraulic and organic loading with MLSS development in ASP during secondary startup operation
DAY	FLOW IN m³/d	INFLUENT BOD mg/l	MLSS mg/l	APPLIED VOL.ORG.LOAD kgBOD/m³/d	F/M RATIO kgBOD/kg/MLSS/d	NUTRIENTS ADDITION
27	108	1430	1500	0.13	0.09	-BOD/N/P of 200/5/1.5 was maintained -Baby food added was 1–3 g/kg BOD in -Groundnut cake; Starting – 2 kg/100 kg BOD and was gradually decreased to 150g/100 kg BOD at the end
32	222	1500	2200	0.28	0.13
34	388	1430	2800	0.46	0.17
36	388	1340	2800	0.43	0.15
42	388	1240	2800	0.4	0.14
48	388	1170	3700	0.38	0.10
54	388	1200	4900	0.39	0.08
60	388	1310	6050	0.42	0.07

6.3 Putting A-B process into operation and performance evaluation

Figure 4 shows the A-B process operation. In addition, Table. 3 shows the data related to the shift inflow from B to A, MLSS development in A and B, influent and effluent COD of both A and B along with the organic loading and F/M ratio from day 61 to 120. On 61st day, 132 m³/d raw wastewater was given to A and 256 m³/d to B with an MLSS concentration 2800 mg/l and 4200 mg/l respectively. Additionally, B received effluent of A, thus receiving a total flow of 388 m³/d. During the subsequent 35 days of operation feed to A was increased by 50 m³/d at 7 days interval and balance of 388 m³/d being fed to B. On 96th day the entire flow of 388 m³/d was received by unit A and its outlet to B, thus achieving flow pattern of A-B process (Fig. 4). On 104th day (43 days of operation) the MLSS was found to be 11400 mg/l in the aeration tank of A that has a volume 900 m³. Average BOD/COD ratio of ten samples (random) collected and analyzed during 77 days was 0.35. BOD/COD ratio of effluent of A was 0.25 and that of B was 0.15. The total BOD stabilized in unit A in 43 days (day 61–104) was 6870 kg (considering average of COD these days and average of BOD/COD ratio of 0.35). Volatile fraction of sludge yielded in A was determined to be 0.6 and thus volatile content of the total sludge was calculated to be 4644 kg. Yield coefficient, Y was found to be 0.68. During 43 days of operation, the influent COD ranged from 1120 to 2530 mg/l; the average being 1940 mg/l. On 104th day the effluent COD of unit A was 90 mg/l and that of B was 80 mg/l. From 104th to 108th day, sludge was harvested from unit A reducing the MLSS from 11400 mg/l to 3600 mg/l. The harvested sludge, 7020 kg was used in the pulping section of the papermill effecting resource recovery. During the subsequent 12 days of operation, flow was increased from 388 m³/d to 488 m³/d. MLSS increased from 3600 mg/l to 7800 mg/l. For an influent COD ranging from 1703 to 1986 mg/l, the effluent COD of A ranged from 550 mg/l to 258 mg/l and that of B ranged from 105mg/l to 78 mg/l. During the 60 days of operation (61–120 days), the volumetric COD loading ranged from 0.35 kg COD/m³/d to 1.09 kg COD/m³/d and F/M ratio ranged from 0.04 to 0.24 kg COD/m³d. Figure 4 shows the variation in influent and effluent COD along with the variation in MLSS.

Table 3

Putting A-B process into operation and performance evaluation (61 to 120 days)
Day	Direct Wastewater Flow in m³/d to		Total Wastewater Flow to B in m³/d	MLSS mg/l of AT of		Influent COD mg/l	Vol.COD.Loading kgCOD/ m³.d (A)	F/M Ratio kgCOD/ kgMLSS.d (A)	Effluent COD mg/l Clarifier of
Day	A	B	Direct + Effluent of A	A	B	Influent COD mg/l	Vol.COD.Loading kgCOD/ m³.d (A)	F/M Ratio kgCOD/ kgMLSS.d (A)	A	B
61	132	256	388	2800	4200	1558	-	-
68	182	206	388	3750	3800	2358	0.35	0.09	510	885
75	233	155	388	3800	4700	1958	0.40	0.11	188	418
82	285	103	388	4400	4100	1974	0.51	0.12	160	680
89	338	50	388	8300	3000	1120	0.35	0.04	95	130
96	388	0	388	9100	5600	2083	0.78	0.08	63 (96%)	151
104	388	0	388	11400	7200	2530	1.09	0.09	90 (96%)	80
108	388	0	388	3600	4700	1986	0.85	0.24	550 (72%)	98
115	438	0	438	5400	4000	1703	0.73	0.13	258 (84%)	78
120	488	0	488	7800	4200	1850	0.9	0.11	275 (85%)	105

The study includes 120 days of reactor operation and performance evaluation. The operations were carried out in three phases. The following conclusions can be drawn from the study.

In the first phase of this study, cow dung rich in microbial consortium were successfully used as a seed material for developing aerobic culture and flocs of good settleability.

On addition 25 kg (dry weight) of fresh cow dung per m³ of fresh ground water as seed and on aeration of the medium with supply of N, P and other micronutrients by addition of baby food and groundnut cake, good flocs were observed on 9th day of operation.

On 10th day the MLSS in the AT was 800 mg/l and the sludge volume was 40 ml/litre with a sludge volume index (SVI) of 50 ml/g. This indicates that the sludge developed was of good settleability.

Addition of nutrients like N, P along with micronutrients through the addition of baby food and groundnut cake from 7th day and 3rd day seem to have accelerated microbial growth and floc formation.

In spite of the second phase cow dung addition of 8 kg (dry weight) per m³ of the medium, the MLSS increase from 10th day to 23rd day was only 300 mg/l whereas addition of a total of 125.5 m³ of wastewater from 23rd day of operation resulted in an increase in MLSS of 400 mg/l by 27th day.

It shall be concluded that up on addition of cow dung at the rate of 25 kg (dry weight) per m³ of medium, as seed, and on addition of N, P and other micronutrients, microbial flocs with good settleability can be obtained within 9 to 10 days of aeration. Once an MLSS of 1000 mg/l in the AT is obtained, organic loading by the addition of wastewater can be started subsequently.

During the second startup operation for 33 days the aerobic bacterial flocs developed from cow dung, known to be rich in cellulose, was successfully fed with wastewater from a paper mill that use waste paper as raw material.

During 33 days of operation, the applied organic loading was increased by increasing the wastewater flow to the AT and as a result the MLSS increased from 1500 mg/l to 6050 mg/l.

During the last 26 days of operation the organic loading was in the range of 0.38 to 0.46 kg BOD/m³/d. In the initial 21 days of operation the MLSS increase was 2200 mg/l whereas during the remaining 12 days, the increase was 2350 mg/l. This initial delay in sludge development shall be attributed to the time required for the acclimatization to the new substrate, here cellulose, which is usually referred to as lag phase of growth.

However, a more specific information on the extend of lag phase could be obtained if the higher organic loading rate was maintained from the initial days itself.

During the 3rd phase of this study, the entire flow of 388 m³/d was made to flow in the A-B process by providing stepwise increase to A, correspondingly reducing direct flow to B in 43 days.

During these 43 days, MLSS in A increased from 2800 to 11400 mg/l. The total BOD stabilized was 6870 kg and sludge yielded in A (volatile fraction) was 4644 kg, resulting in a yield coefficient, Y of 0.68.

In 4 days since 104th day, 7020 kg (dry weight) was harvested and utilized in the pulping section.

During 12 days of operation from 108th day, effluent COD of A ranged from 550 mg/l to 258 mg/l, effluent COD of B ranged from 105 mg/l to 78 mg/l where the influent COD ranged from 1986 mg/l to 1703 mg/l and flow increased from 388 m³/d to 488 m³/d.

The volumetric loading was in the range of 0.73 to 0.9 kg COD/m³.d and F/M ratio was in the range of 0.11 to 0.24 kg COD/kg MLSS in A.

Ethical approval

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Consent to participate

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Consent to publish

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Authors contributions

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Kochu Thresya Sojan and Dr. Grasius Mattamana Geevarghese. Kochu Thresya Sojan and Dr. Grasius Mattamana Geevarghese together wrote the manuscript. All Authors read and approved the final manuscript.

Funding

No funding was received

Competing interests

Financial interests: Kochu Thresya Sojan declare she has no financial interests. Dr Grasius Mattamana Geevarghese is consultant to CSons Paper Mills Pvt. Ltd.; Puthupady PO, Ernakulam district, India.

Non-financial interests: none.

Availability of data and materials

All data generated or analysed during the present study are not included in this published article. Only the data pertaining to the manuscript is included.

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Reviewers agreed at journal
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Speedy Mlss Development From Cow Dung, Wastewater Treatment and Sludge Recovery From the Activated Sludge Process (a-b Process) of a Paper Mill That Use Waste Paper as Raw Material - A Case Study

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Version 1

Abstract

Figures

1. INTRODUCTION

2. A-B PROCESS

3. OBJECTIVE

4. METHODOLOGY

5. MATERIALS AND METHODS

5.1 MATERIALS

5.2 METHODS

5.2.1 Different phases of reactor operation

5.2.2 Analytical Techniques

6. RESULTS AND DISCUSSION

6.1 Operations for 27 days

6.2 Reactor operations from 27th – 60th day (secondary startup) and reactor performances

6.3 Putting A-B process into operation and performance evaluation

7. CONCLUSION

Declarations

References

Status:

Version 1