Restoration Study of Microorganisms in Lake Water Purification

doi:10.4236/eng.2013.510B094

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Engineering, 2013, 5, 459-462

http://dx.doi.org/10.4236/eng.2013.510B094 Published Online October 2013 (http://www.scirp.org/journal/eng)

Restoration Study of Microorganisms in

Lake Water Purification

Fang Yang, Rui Zhu

Hebei Electric Power Design & Research Institute, Shijiazhuang, China

Email: z hurui [email protected], [email protected]

Received 2013

ABSTRACT

We screened the bacteria with restoration and purification functions in lake water and found that, Bacillus subtilis had

the highest water purification ability. Photosynthetic bacteria, lactobacillus bacteria, nitrifying bacter ia and oligotrophic

bacteria also showed different levels of lake water purification and restoration. L1873 orthogonal experiments were de-

signed to optimize the ratio of complex agents to get the best ratio of various bacteria as 10 g/L Bacillus subtilis, 2 g/L

photosynthetic bacteria , 0.8 g/L lactobacillus , 0.6 g/L nitrifying b acteria 1, 0.4 g/L nitrifying bacteria 2 and 0.6 g /L oli-

gotrophic bacteria. When lake water was purified for 30 d under this ratio, total phosphorus content decr eased 85.90%,

total nitrogen content decreased 70.96%, and COD value decreased 81.19%.

Keywords: Water Purification Microorganisms; COD; Total Phosphorus; Total Nitrogen

1. Introduction

Due to the impacts of human life and pollution, nitrogen,

large amounts of phosphorus and other nutrients entered

into the lake [1]. This causes rapid growth of algae and

other plankton, decreased dissolved oxygen in water bo-

dies, deteriorated water quality, and massive death of fish

and other organisms; this phenomenon is known as water

bloom of lake water. The major components that cause

lake water bloom were phosphorus, nitrogen and organic

carbon [2]. The microbial water purification and restora-

tion rely mainly on microbial metabolism for th e purpose

of deaminase, dephosphorization and carbon transfer to

purify and r e stor e water bodies [3].

Lake water is generally hydrostatic water and more

prone to eutrophication, which is further exacerbated by

the plant nutrients imputs from industrial wastewater,

domestic sewage and agricultural runoff. It is hard to

solve the eutrophication of lake solely re ly ing on the self-

purification of lake water, and lake eutrophication is ur-

gent to be solved [4,5].

In this study, we screened the bacteria strains with

restoration and purification functions in lake water and

studied the ratio of bacteria agents in order to obtain the

microbial agents with significant purification and resto-

ration effects on lake water.

2. Materials and Equipment

2.1. Materials and Strains

Lake water was obtained from Hengshui Lake at Nation-

al Wetland Nature Reserve; Bacillus subtilis, Photo-

synthetic bacteria, Lac tob acillus bacteria, Nitrifying bac-

teria and Oligotrophic bacteria were preserved by our

laboratory.

2.2. Instruments

Multi-parameter water quality analyzer was purchased

from Hualian Technology Co., Ltd. (5b-6c).

3. Methods

3.1. Determination of the Total Number of

Bacteria

The number of bacteria was determined by plate count-

ing method.

3.2. Determination of Total Nitrogen

Total nitrogen was determined as described in “Alkaline

potassium persulfate digestion ultraviolet spectrophoto-

metry determination of water quality total nitrogen”

(GB11894-89).

3.3. Determination of Total Phosphorus

Total phosphorus was determined as described in “Am-

monium molybdate spectrophotometry determination of

water quality total phosphorus ” (GB 11893-89).

3.4. Determination of COD

CODMn was determined as described in “protein-per-

F. YANG, R. ZHU

460

manganate index determination” (GB11892-89).

3.5. Microorganism Culture

1) Seed culture media

Seed culture media for Bacillus subtilis, photosynthet-

ic bacteria, lactobacillus bacteria, nitrifying bacteria and

were beef extract peptone medium.

2) Proliferation mediu m (g/L): glucose 1, yeast extract

0.7, peptone 1, (NH4)2SO4 0.2, MgSO4·7H2O 0.2, KH2PO4

1, and agar 18 g, pH 7.2.

3.6. Screening of Lake Wat er Rest oration and

Purification Bacteria

According to information reported in literature, microor-

ganisms with w ater restoration and purification functions,

Bacillus subtilis, photosynthetic bacteria, lactobacillus

bacteria, nitrifying bacteria 1, nitrifying bacteria 2 and

oligotrophic bacteria, w ere sel ected, and total phosphorus,

total nitrogen and COD value in lake water were meas-

ured. Lake water from same position was selected and

aliquoted into 7 1L-flasks. The adding amount of micro-

organisms were: 6 g /L Bacillus subtilis, 2 g/L photosyn-

thetic bacteria, 0.4 g/L lactobacillus, 0.2 g/L nitrifying

bacteria 1, 0.2 g/L nitrifying bacteria 2, and 0.4 g/L oli-

gotrophic bacteria, with plain water as control. Different

water indicators in lake wa ter wer e determined 20 d after

adding agents, a nd the measure temperature was 20˚C.

3.7. Design of Orthogonal Experiment for

Complex Agent s Ratio

According to relevant experimental reports and conven -

tional value, orthogonal experiments were preformed

mainly using Bacillus subtilis with five other supple-

mental microorganisms, each containing three concentra-

tions (L1873). The level of orthogonal design factors was

shown in Table 1.

4. Results and Discussion

4.1. Screening of Lake Wat er Rest oration and

Purification Bacteria

According to relevant literature, six kinds of microor-

ganisms with lake water purification and r estoration abil -

ity were selected for pilot study. Related indicators were

measured, and the re sults were shown in Figure 1.

As shown in Figure 1, 20 d after adding agents, total

phosphorus, total nitrogen and COD values in each water

sample revealed that all six bacteria had different levels

of water pur ification and restor ation ability. Bacillus s ub-

tilis had strongest purificatio n ability of total phosphorus

purification, lactobacillus had higher ability of nitrogen

purification, and photosynthetic bacteria higher ability

Table 1. L18(37) orthogonal experimental design.

level Factors

A(g/L) B(g/L) C(g/L) D(g/L) E(g/ L) F(g/L) G

1 6 1 0.4 0.2 0.2 0.4 1

2 8 2 0.6 0.4 0.4 0.6 2

3 10 3 0.8 0.6 0.6 0.8 3

Notes: A: Bacillus subtilis; B: Photosynthetic bacteria; C: Lactic acid bac-

teria; D: Nitroba cte ria 1; E : Nitrobacteria 2; F: Oligotrophic bacteria; G: Error.

The total phosphorus

The total nitrogen

COD

The total phosphorus (mg/L). The total nitr ogen (mg/L). COD (mg/L)

A: The initial quality of lake water

B: The quality for lake water of adding Bacillus subtilis

C: The quality for lake water of adding Photosynthetic bacteria

D: The quality for lake water of adding Lactic acid bacteria

E: The quality for lake water of adding Nitrobacteria 1

F: The quality for lake water of adding Nitrobacteria 2

G: The quality for lake water of adding Oligotrophic bacteria

Figure 1. The purifying and repairing bacteria screening

for lake water.

of COD purification. Comprehensive analysis of three

measured indicators to compare to the purification ability

of each bacterium showed that Bacillus subtilis group

exhibited strongest water purification capability. Ac-

cording to the purification characteristics of each bacte-

rium, we used a complex agent based on Bacillus subtilis

with five other supplemental bacteria as purification

agents for studies.

4.2. Ratio of Complex Agent

Using COD value as L1873 orthogonal experiment results,

complex agent was added and the results were deter-

mined 20 d later, as shown in Table 2.

As shown in Tables 2 and 3, the ratio difference of

various agents had high impacts on the measured COD

values. Among each agent ratio, Bacillus subtilis and

nitrifying bacteria displayed highly significant impacts,

and lactobacillus and oligotrophic bacteria had signifi-

cant impacts. According to the F value, the order of im-

pacts of each bacteria on COD was: Bacillus subtilis >

F. YANG, R. ZHU

461

Table 2. Visual analysis for L18(37) orthogonal experimental

design.

Number

of test

Factors COD

(mg/L)

A B C D E F G

1 1 1 1 1 1 1 1 16.91

2 1 2 2 2 2 2 2 17.32

3 1 3 3 3 3 3 3 15.25

4 2 1 1 2 2 3 3 13.05

5 2 2 2 3 3 1 1 11.25

6 2 3 3 1 1 2 2 10.85

7 3 1 2 1 3 2 3 7.22

8 3 2 3 2 1 3 1 7.35

9 3 3 1 3 2 1 2 7.38

10 1 1 3 3 2 2 1 5.36

11 1 2 1 1 3 3 2 7.9

12 1 3 2 2 1 1 3 9.53

13 2 1 2 3 1 3 2 7.52

14 2 2 3 1 2 1 3 7.9

15 2 3 1 2 3 2 1 8.82

16 3 1 3 2 3 1 2 7.65

17 3 2 1 3 1 2 3 5.27

18 3 3 2 1 2 3 1 6.81

K1 12.05 9.62 9.89 9.60 9.57 10.10 9.42

K2 9.90 9.50 9.94 10.62 9.64 9.14 9.77

K3 6.95 9.77 9.06 8.67 9.68 9.65 9.70

R 5.10 0.28 0.88 1.95 0.11 0.96 0.35

Table 3. The variance analysis for mycelium production.

Factors The square

of deviations Free

degree F The critical

value of F Significance

A 78.627 2 2125.054 19.000 ****

B 0.228 2 6.162 19.000

C 2.933 2 79.270 19.000 *

D 11.397 2 308.027 19.000 **

E 0.037 2 1.000 19.000

F 2.787 2 75.324 19.000 *

G 0.423 2 11.432 19.000

Error 0.04 2

nitrifying bacteria 1 > lactobacillus > oligotrophic bacte-

ria > photosynthetic bacteria > nitrifying bacteria 2. Ac-

cording to the K value, the best bacteria combination was:

A3B2C3D3E2F2, i.e. 10 g/L Bacillus subtilis, 2 g/L photo-

synthetic bacteria, 0 .8 g/L lactobacillus, 0.6 g/L nitrify-

ing bacteria 1, 0.4 g/L nitrifying bacteria 2, and 0.6 g/L

oligotrophic bacteria. It is proved by experiments that

under th is condition, the COD value at 20 d after adding

complex agents was 5.13 mg/L, which was lower than

the minimal value in orthogonal experimental design.

Comparing with the COD value in original lake water

sample, the number decreased 81.15%.

4.3. The Impact of Compl ex Agent on Total

Phosphorus Reduction

Complex agen t in optimal ratio was added into lake wa-

ter, total phosphorus content in lake water was measured

every 5 d. The results were shown in Fi gure 2.

As shown in Figure 2, aft e r complex agent in optimal

ratio was added into lake water, the total phosphorus

content in lake water quickly declined in 10 d. Between

10 d and 30 d, the total phosphorus content decreased,

but in a slow rate. Within the experimental period, the

lowest total phosphorus content was observed at 30 d,

with the minimal value of 0.11 mg/L and the relative

reduction of 85.90%, indicating that addition of complex

agent in this ratio can effectively reduce the phosphorus

content in lake water.

4.4. The Impact of Complex Agent on Total

Nitrogen Reduct ion

Complex agent in optimal ratio was added into lake wa-

ter, total nitrogen content in lake water was measured

every 5 d. The results were shown in Figure 3.

As shown in Figure 3, af ter co mplex agent in optimal

ratio was add ed in to lake w ater , the total nitrogen content

in lake water quickly declined in 20 d then slowly de-

creased. Within the experimental period, the lowest total

nitrogen content was observed at 30 d, with the minimal

value of 4.03 mg/L and the relative reduction of 70.96%,

The total phosphorus (mg/L)

0.0

The total phosphorus

Days

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Figure 2. The complex agent effect to total phosphorus of

lake water.

F. YANG, R. ZHU

462

indicating that the complex agent in this ratio had good

effects on reducing nitrogen content in lake water.

4.5. The Impact of Complex Agent on COD

Value

Complex agen t in optimal ratio was added into lake wa-

ter, COD value in lake water was measured every 5 d.

The results were shown in Figure 4.

As shown in Figure 4, when adding complex agent in

optimal ratio, the COD value showed highest reduction

extent in the first 20 d, which may be because the better

effects and higher activity of complex agent during this

period. After 20 d, the COD valu e in lake water decreased

slightly, but remained similar. A t 30 d, the COD value in

lake wat er was lowest, with the minimal value of 5.13

mg/L and the relative reduction of 81.89% comparing to

The total ni t rogen (mg/L)

The total nitrogen

Days

Figure 3. The complex agent effect to total nitrogen of lake

water.

COD (mg/L)

COD

Days

Figure 4. The complex agent effect to COD of lake water.

no complex agents control, indicating that addition of

complex agent in this ratio can effectively reduce the

COD value in lake water.

5. Conclusion

Eutrophication can cause deteriorated water quality and

reduced level of dissolved oxygen in water, wh ich af-

fected the living of water creatures. Application of mi-

croorganisms for water purification and restoration can

effectively purify water. Through the screening of bacte-

ria with water restora tion and purification capacity show-

ed that Bacillus subtilis had strongest water purification

ability, and other bacteria had different levels of impacts

on water purification and restoration. Using L1873 or-

thogonal experimental design to optimize the ratio of

complex agents, we got the optimal ratio of each bacteria

was: 10 g/L Bacillus subtilis, 2 g/L photosynthetic bacte-

ria, 0.8 g/L lactobacillus, 0.6 g/L nitrifying bacteria 1, 0.4

g/L nitrifying bacter ia 2 and 0.6 g/L oligotrophic b acteria.

When lake water was purified for 30 d under this ratio,

total phosphorus content decreased 85.90%, total nitro-

gen content decreased 70.96%, and COD value decreased

81.19%. These indicated that complex agent in this ratio

can effectively reduce the total phosphorus, total nitrogen

and COD value in lake water with good purification ef-

fect on lake wate r.

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