An experiment was carried out to investigate the performance of mixed ocean bacteria, isolated from the ocean sediment, on landfill leachate treatment. In this treatment, ocean bacteria were the only constituent added to remove organics and NH4+-N. Given their considerable influence on wastewater purification, factors such as inoculum, initial pH, processing time and oxygen condition, were directly involved in this research. As indicated by laboratory test results, chemical oxygen demand (CODCr) and NH4+-N removal could reach 94.45% and 67.87%, respectively, after 3 days of treatment, in conditions of natural pH 6.3 and with the application of oxygen. The volt–ampere characteristics of the bacteria solution verified the redox-active ability of the bacteria in landfill leachate treatment.

INTRODUCTION

Landfill leachate, one of the main problems resulting from sanitary landfill, has quickly produced a considerable an increase in quantities of solid waste in China (Bing et al. 2008). Being high-strength wastewater, it is characterized by extremes of high chemical oxygen demand (CODCr), inorganic salts, heavy metals and toxicity. The composition of the leachate is based on the age of the landfill, local rainfall, composition and degree of contouring, compacting of solid wastes and physicochemical conditions at the landfill (Gotvajn et al. 2009). Therefore, young landfill leachates present distinct features during treatment compared to that of older landfill leachates. Many different organic and inorganic compounds are contained in the leachate; these may be either dissolved or suspended and biodegradable and non-biodegradable (Bilgili et al. 2008). If not disposed of safely, landfill leachate can provide a major source of water contamination, because it can cause high pollution in the receiving water as it percolates through soil and subsoil (Oman & Junestedt 2008). Thus, to minimize water resources pollution and to avoid acute and chronic toxicities, leachate treatment before discharge should be enforced by legal requirement.

To overcome the considerable negative impacts of landfill leachate on the environment, several techniques have been reported for treating this wastewater (Renou et al. 2008), which include biological treatment (Lim et al. 2012; Capodici et al. 2014), physical treatment, such as flotation (Zouboulis et al. 2003) and absorption (Wang et al. 2002), chemical treatment, such as precipitation (Kim et al. 2007) and new treatments, such as membrane processes (Piatkiewicz et al. 2001). Biological treatment is an environmentally friendly technique for wastewater treatment. Orupoald et al. (2000) studied the biological treatment of leachate from oil shale semicoke ash heaps in a wastewater lagoon using laboratory-scale batch processes; the best COD removal was up to 70.45% for 10 days in the intermittently aerated batch. It indicated that leachate could be treated in an aerated lagoon system, and that even for high pH leachate, the treatment is feasible without pH adjustment.

In this study, aerobic biological treatment of landfill leachate was investigated in batch. Since ocean marine sediment includes diverse bacteria, which can survive even in extreme deep-sea environments, they were chosen as inocula and used innovatively to treat landfill leachate. A flask reactor was filled with landfill leachate and fixed in a digital biochemical incubator to remove contaminants. The objective of the study was to investigate performance on organics and removal in landfill leachate treatment, without the addition of extra inorganic or organic nutrients.

MATERIALS AND METHODS

Landfill leachate

The landfill leachate, without any efficient bacteria, was collected from a local landfill site in Dalian, Liaoning Province of China, and stored at 4 °C in a plastic container. Analysis results showed that the landfill leachate before treatment had a pH value of 6.3, and the concentration of each composition is listed in Table 1.

Table 1

Leachate composition before treatment

Composition NH4+-N CODCr TP TN TKN BOD5 
Concentration (mg/L) 168.45 ± 25 6,636 ± 478 77.2 ± 6 256.34 ± 20 183.67 ± 34 2,948 ± 232 
Composition NH4+-N CODCr TP TN TKN BOD5 
Concentration (mg/L) 168.45 ± 25 6,636 ± 478 77.2 ± 6 256.34 ± 20 183.67 ± 34 2,948 ± 232 

TKN = total Kjeldahl nitrogen.

Data reported in Table 1 provide a biochemical oxygen demand/chemical oxygen demand (BOD/COD) ratio equal to 0.44, which in respect of landfill leachate is representative of a leachate derived from a young landfill; it also shows that the leachate treated in this study is relatively highly biodegradable.

Bacterial suspension

Different ocean sediment samples (from the China Ocean Biologic Sample Repository, Qingdao, Shandong Province, China) were added to landfill leachate without adding any other elements. When bacteria in the sediment sample cultured, by shaking for 5 days, it was transferred to fresh landfill leachate medium for another 5 days to screen effective bacteria with an excellent ability to remove organics and from the landfill leachate. The effective ocean bacteria were inoculated to fresh leachate medium for 3 days for bacteria enrichment. Afterwards, the leachate medium was centrifugalized at a speed of 12,000 rpm for 10 min, and was then filtered through a membrane. The cells were washed off with sterile physiological NaCl solution (mass fraction 0.7%). Moreover, the cells were diluted in sterile phosphate buffer (pH = 7.0), where the OD510 density of bacterial suspension was 2.21. The bacterial suspension was then stored at 4 °C for later utilization in the batch experiments. As a control group, the same inoculum was cultivated in saline water for 3 days. The effects of water type on the growth of the ocean bacteria are shown in Table 2.

Table 2

Effect of water on the growth of the ocean bacteria

Water type (g/L) Landfill leachate Seawater 
Biomass (OD5102.14 2.51 
Water type (g/L) Landfill leachate Seawater 
Biomass (OD5102.14 2.51 

Experimental procedures

The experiments were carried out in batch mode. First, the desired amount of bacteria suspension was added to the 100.0 mL sample leachate in the flask fixed to the digital biochemical incubator (HZQ-F160, ETD Co., Ltd, Ningbo, China). After the desired duration, 10-mL post-processing leachate samples were centrifuged (GT16-3, TBL Co., Ltd, Beijing, China). Then, the CODCr, , and concentrations of the supernatant were analyzed. Repeated experiments were carried out, and the results were obtained in triplicate within (±5%) data deviation. The initial pH of the landfill leachate was adjusted with diluted HCl or NaOH solution.

Analyses and calculations

Total phosphorus (TP), total nitrogen (TN), ammonia nitrogen , nitrate nitrogen and nitrite nitrogen were measured as described previously (APHA 1998). The pH of the leachate was recorded by pH meter (pHXS, REC, Shanghai, China). Optical density at wavelength 510 nm (OD510), detected by ultraviolet-visible spectrophotometer (UV-1,750, Mfg Co., Ltd, Tokyo, Japan) was used to characterize the cell concentration. The CODCr was measured by COD Digital Reactor Block (South China Institute of Environment Sciences, MEP, Guangzhou, Guangdong Province, China). Contaminant removal ratios post-treatment were calculated by Equation (1) 
formula
1
C1 and C2 are the initial and the post-processing CODCr concentrations of the supernatant collected after centrifugation (mg/L), and V1 and V2 are the volume (litre) of landfill leachate and that of bacterial suspension mixed with leachate, the values of which are 0.1 and 0.12, respectively.

Voltammetry incorporates three electrodes: a working electrode (Pt/C electrode), a reference electrode (calomel electrode) and a counter electrode (Pt electrode) at 25 °C with a scanning rate of 50 mV per min, pH = 7.

RESULTS AND DISCUSSION

Inoculum dose

To investigate the effect of inoculum dose on landfill leachate treatment, experiments were carried out. As can be seen in Figure 1, after 3 days, with inoculum dose in a range 0–10% (V/V), cell concentration (OD510), the CODCr and removal ratio dramatically increase with increasing inoculum. With an inoculum boost of more than 10%, CODCr and removal ratios change very little. These results indicate that ocean bacteria utilize the organic carbon and in the leachate for bacterial reproduction, while removing contaminants. This considerable efficiency in removing organics and may be mainly due to efficient microorganisms (Shalaby 2011), which probably occur in the ocean bacteria. For the leachate sample without ocean bacteria inoculation, the CODCr removal reached 30% after 3 days of processing, which was much lower than that of any other groups with ocean bacteria inoculation. This proves that there are no efficient bacteria in the untreated landfill leachate.

Figure 1

Effect of bacteria inoculum on landfill leachate treatment, where conditions were pH = 6.3 with oxygen for 3 days.

Figure 1

Effect of bacteria inoculum on landfill leachate treatment, where conditions were pH = 6.3 with oxygen for 3 days.

Optimal pH

The effect of the initial pH within the range of 3.0–9.0 on landfill leachate treatment was also studied. As can be observed in Figure 2, the pH of leachates ranges from 3.0–4.0, with little difference on increasing OD510 and CODCr removal efficiency, which reveals that the heterotrophic bacteria are inhibited by heavily acidic conditions, and chemoautotrophic bacteria can use as a nutrient to remove . However, with increasing pH, ocean bacteria can actively reproduce and degrade contaminants. The high CODCr and removal reached 94.45% and 63.56%, respectively, at a pH of 5.0–10.0 after 3 days. It indicates that bacteria can work efficiently at a pH = 7 value which benefits water discharge. The contaminant removal ratio through this biological method is much more desirable compared to precipitation of landfill leachate. With precipitated ammonium ions, for example magnesium ammonium phosphate (Yangin et al. 2002), its maximum removal of 66–85% was achieved at pH 9.3–11.0. A larger alkali dose consumption is demanded, and the treated leachate pH needs to be adjusted before discharge.

Figure 2

Effect of pH on the landfill leachate treatment, where conditions were inoculum dosage of 10% with oxygen applied for 3 days.

Figure 2

Effect of pH on the landfill leachate treatment, where conditions were inoculum dosage of 10% with oxygen applied for 3 days.

Processing time

Figure 3 shows the effect of different processing times (h) on CODCr removal. As can be seen in Figure 3, in the first 24 h, CODCr removal reaches 76.23%. After another 24 h, it increases to 93.71%. It is interesting to note that processing time after 48 h makes little contribution to removing contaminants. The reason may be due to lack of carbon source or refractory organic residue. In terms of CODCr and removal ratio, this method of biodegradation by shaking is better than chemical oxidation (Qureshi et al. 2002) and adsorption (Kargi & Pamukoglu 2004). However, the CODCr and removal rate is much lower than with chemical oxidation.

Figure 3

The effect of treatment time on leachate treatment, where conditions were inoculum dosage of 10% at natural pH 6.3 with oxygen applied.

Figure 3

The effect of treatment time on leachate treatment, where conditions were inoculum dosage of 10% at natural pH 6.3 with oxygen applied.

Oxygen conditions

To study the ocean bacteria, the effect of oxygen being supplied or not on landfill leachate treatment was studied, and results are shown in Figure 4. Figure 4 shows that, under the condition of oxygen supplied, the bacteria density (OD510), COD removal and removal ratios of the treated leachate dramatically increase, but under the condition without oxygen supplied, ratios hardly increased. This reveals that the mixed ocean bacteria are aerobic micro-organisms. Therefore aerobic processing of landfill leachate favours biodegradable organic pollutants and also ammonium nitrogen (Renou et al. 2008).

Figure 4

The effect of oxygen on bacterial activity, where conditions were inoculum dosage of 10% at natural pH 6.3 for 3 days treatment.

Figure 4

The effect of oxygen on bacterial activity, where conditions were inoculum dosage of 10% at natural pH 6.3 for 3 days treatment.

The mechanism of NH4+-N depletion

As can be seen in Figure 5, under the condition of aeration, concentration decreases, concentration first increases then decreases, and concentration increases with increasing time. These results are probably due to the mixed bacteria containing nitrite oxidizing bacteria and nitrobacteria. With nitrite oxidizing bacteria in the leachate, ammonia was oxidized to nitrite, which was quickly oxidized to nitrate by nitrobacteria. It can therefore be inferred that the mechanism of depletion is ammonia oxidation (Han et al. 2013).

Figure 5

The mechanism of depletion.

Figure 5

The mechanism of depletion.

Volt–ampere characteristics curve of the bacteria

An experiment was carried out to observe the volt–ampere characteristics of the bacteria solution. As can be seen in Figure 6 for curve 1, there are reductive peaks where the potential is −0.599 V and an oxidation peak where the potential is 0.148 V. The ratio of Irp (current of reductive peak) to Iop (current of oxidation peak) is about 1, which indicates that the group with bacteria, compared to the control group without bacteria, has an apparent redox peak. This proves that the electrochemical activity of the ocean bacteria can play a major role in landfill leachate treatment.

Figure 6

The volt–ampere characteristics of the ocean bacteria.

Figure 6

The volt–ampere characteristics of the ocean bacteria.

CONCLUSIONS

In landfill leachate treatment without any external carbon addition, it is feasible that ocean bacteria utilize organics as the only carbon source to efficiently remove carbon and . In the experiments, the steady ammonia removal performance may be attributed to the enrichment of bacteria in mixed ocean bacteria, which showed high nitrogen-removal capacity.

Utilization of marine bio-resource to treat landfill leachate is not only a significant outcome, but also the most fundamental initial stage of an effective method for wastewater treatment, as the success of the latter is based on the former. The paper has established this by defining the baseline study in the landfill leachate context, and also by indicating the implications of marine bio-resource exploitation.

ACKNOWLEDGEMENTS

This research was supported by the China Ocean Mineral Resource R&D Association (No. DY125-15-T-08), the National Natural Science Foundation of China (No. 21176242 and No. 21176026), and the National High Technology Research & Development Program (863 program) of China (No. 2012AA062401).

REFERENCES

REFERENCES
APHA (American Public Health Association)
1998
Standard Methods for the Examination of Water and Wastewater
,
22nd edn
.
American Public Health Association
,
Washington, DC, USA
.
Aziz
H. A.
Yussff
M. S.
Adlan
M. N.
Adnan
N. H.
Alias
S.
2004
Physicochemical removal of iron from semi-aerobic leachate by limestone filter
.
Waste Management
24
,
353
358
.
Bilgili
M. S.
Demir
A.
Akkaya
E.
Ozkaya
B.
2008
COD Fractions of leachate from aerobic and anaerobic pilot scale landfill reactors
.
Journal of Hazardous Materials
158
,
157
163
.
Bing
X.
Xingpeng
C.
Hongyan
L.
2008
Analysis of transition process from waste management towards resource management system
. In:
Wireless Communications, Networking and Mobile Computing, 2008, 4th International Conference, 12–14 October 2008, IEEE, Dalian, China
.
Gotvajn
A. Z.
Tisler
T.
Zagorc-Koncan
J.
2009
Comparison of different treatment strategies for industrial landfill leachate
.
Journal of Hazardous Materials
162
,
1446
1456
.
Orupoald
K.
Tenno
T.
Henrysson
T.
2000
Biological lagooning of phenols-containing oil shale ash heaps leachate
.
Water Research
34
(
18
),
4389
4396
.
Piatkiewicz
W.
Biemacka
E.
Suchecka
T.
2001
A polish study: treating landfill leachate with membranes
.
Filtration and Separation
38
,
22
26
.
Qureshi
T. I.
Kim
H.-T.
Kim
Y.-J.
2002
UV-catalytic treatment of municipal solid-waste landfill leachate with hydrogen peroxide and ozone oxidation
.
Chemical Engineering Journal
10
,
444
449
.
Renou
S.
Givaudan
J. G.
Poulain
S.
Dirassouyan
F.
Moulin
P.
2008
Landfill leachate treatment: review and opportunity
.
Journal of Hazardous Materials
150
,
468
493
.
Shalaby
E. A.
2011
Prospects of effective microorganism technology in wastes treatment in Egypt
.
Asian Pacific Journal of Tropical Biomedicine
1
(3)
,
243
248
.
Wang
Z.-P.
Zhang
Z.
Lin
Y.-J.
Deng
N.-S.
Tao
T.
Zhuo
K.
2002
Landfill leachate treatment by a coagulation-photooxidation process
.
Journal of Hazardous Materials
95
,
153
159
.
Yangin
C.
Yilmaz
S.
Altinbas
M.
Ozturk
I.
2002
A new process for the combined treatment of municipal wastewaters and landfill leachates in coastal areas
.
Water Science and Technology
46
,
111
118
.
Zouboulis
A.
Jun
W.
Katsoyiannis
A.
2003
Removal of humic acids by flotation
.
Colloids and Surface A: Physicochemical Engineering Aspects
231
,
181
193
.