INFLUENCE OF SEWAGE SLUDGE ON CONTENT AND INTAKE OF TRACE ELEMENTS BY GRASS RECLAMATION MIXTURES

Józefa Wiater, Aleksander Kiryluk, Adam Łukowski
Department of Technological Research, Technical University in Białystok, Poland

ABSTRACT

Study was carried out on local municipal dumping ground in Stożne near Kowale Oleckie in 2001 and 2002. The efficiency of grass mixtures in sodding was tested on a base of a two-factor field experiment: D – sewage sludge – three doses (20, 40 and 60 DM kg · 10 m^-2). Five different grass mixtures and Festulolium in pure sowing were applied. Plant samples were taken in 2001 and 2002. After digestion of plants in microwave digester, iron, manganese, zinc, copper, cadmium, lead, nickel and cobalt contents were determined by means of AAS technique. Then intake of these elements by particular mixtures from 10 m² area was calculated.

It was found that sewage sludge from municipal dumping ground could be utilized for cover fertilization to form a sod. Mixtures No 4, 5 and Festulolium in pure sowing efficiently protected the heavy metal migration into the environment.

Key words: municipal dumping, heavy metals, grass species, sludge rate.

INTRODUCTION

Natural and agricultural utilization of sewage sludge is one of techniques to make them safe [8, 10]. About one third of sewage sludge is utilized in European Union countries as well as in the USA [11]. Sewage sludge contains much organic matter (about 600 g·kg^-1 DM, on average) [1]. However, great amounts of organic matter does not determine its common application in agriculture, mainly due to excessive levels of heavy metals that decrease the quality of cultivated plants and polluting the soil. Among heavy metals there are necessary elements for plants (Cu, Mn, Zn), strongly toxic ones (Cd, Hg, Pb, Ni, As), as well as polyaromatic hydrocarbons (PAH’s) [1]. Heavy metal accumulation is mainly through plant roots [3]. Their application to fertilize the cover of reclamated municipal dumping grounds can be an alternative [6]. In a case of sewage sludge applied onto the reclamated dumping grounds, the contents of toxic elements in the soil and plant material need not fulfill any legal criteria. Among many species used during the process of biological reclamation, Poaceae family appears to be very efficient. Grasses, due to great adaptation abilities to changing habitat conditions, can successively sod reclamated areas [9]. Modern engineering technologies consider the application of plant covers of lawn character for dumping ground reclamation [7]. Grasses are characterized with great ability to accumulate the heavy metals, therefore they play an important role in protection against further migration into the soil and water environment. Thus, it is not aimless to search for proper grass mixtures for common application during biological reclamation of degraded areas.

MATERIAL AND METHODS

Study was carried out on local municipal dumping ground in Stożne near Kowale Oleckie in 2001 and 2002. The efficiency of grass mixtures in sodding was tested on a base of a two-factor field experiment: D_1-3 – sewage sludge – three doses (20, 40 and 60 DM kg · 10 m^-2). Control object without fertilization (D₀) was also introduced. Each object was treated in three replications; every plot area was 10 m². Five different grass mixtures and inter-genus hybrid Festulolium (M6) were applied in every object (Tab.1).

Commonly occurring grass species and inter-genus hybrid Festulolium were applied in experiments. Elevated seed amounts – even to 230 kg·ha^-1 – were used. Sewage sludge was dehydrated and originated from purification plant in Kowale Oleckie. Technological process consisting in fermentation and dehydration allows setting the dry matter at about 15%. Chemical composition of sewage sludge is presented in Tab. 2.

The sewage sludge was introduced onto the no-soil ground in spring 2001. In April, plants were sown. In autumn (September), plants were cut for the first time. Following cut was done in June 2002.

Plant samples, after drying at 70°C, were grinded in titanium-rotor mill and stored in plastic bags. After digestion using microwave digester, contents of iron, manganese, zinc, copper, cadmium, lead, nickel and cobalt were determined by means of AAS technique. At the same time, water content was determined at 105°C. Results were recalculated onto dry matter content and given as a mean value from three replications. Then intake of these elements by particular mixtures from 10 m² area was calculated. Biomass value obtained in this experiment and given by Kiryluk (in press) was used for calculations. Results were statistically worked out taking into account two factors: doses (D) and mixtures (M). k-fold variance analysis for cross-classification was applied. Results were evaluated using Tukey’s test.

RESULTS AND DISCUSSION

Trace element contents in plant dry matter were more depended on fertilization with sewage sludge than the type of mixtures applied (Tab. 3 and 4).

Iron. Collected material contained similar level of iron in every object in 2001. In the second year, plants harvested from objects with sewage sludge treatment contained significantly more iron than control. Successive interaction significantly affected the element accumulation, because plants collected in the second year contained more iron by over 200 mg as compared to previous year, on average. Mixtures M3 and M1 contained the most iron in the first year, and M3, M4 and M5 in the second year. Harkot [5] emphasized that neighboring of species affects the trace element accumulation by grasses.

Manganese. Similar levels of manganese were observed in plants in 2001 and 2002. The influence of the amount of introduced sewage sludge dose on the component content in plants was significant in the second year. Clear increase of manganese content occurred in plants from objects with higher rates of sewage sludge (40 and 60 kg). Mixture M3 was distinguished in the first, and M3 and M4 in the second year of study referring to the element accumulation. Czarnecki and Harkot [2] proved that Festuca rubra accumulated the highest level of manganese in relation to other grass species. This species was the component of studied mixtures.

Zinc. Zinc content in plants collected both in the first and the second year significantly depended on sewage sludge rate. In relation to the object without sewage sludge, the component concentration in plants from object with 20 kg DM per 10 m² increased by 55 mg (2001) and by 28 mg (2002). Higher zinc levels were also recorded in plants treated with higher sewage sludge doses, but the differences among plants that were treated, were insignificant. Wołoszyk and Krzywy [12] stated that Lolium cultivated on sewage sludge accumulated much more zinc as compared to Lolium from control object. Direct action of sewage sludge affected the higher zinc content in mixtures (86.5 mg Zn·kg^-1 DM, on average) than during successive action (55.8 mg Zn·kg^-1 DM). The highest zinc concentration was found in a case of mixture M3 in plants harvested both in 2001 and 2002.

Copper. Copper concentration was higher as a result of direct interaction of sewage sludge than in successive action. Significant influence of sewage sludge on the component content in plants was observed. In 2001 and 2002, the increase of copper concentration was directly proportional to sewage sludge doses applied. However, copper level in tested plants was lower than NiedŸwiecki et al. [9]. found. These researchers applied much higher sewage sludge rates on no-soil grounds and probably therefore they recorded higher concentration of copper in grass mixture. Gorlach and Gambuœ [4] stated that plants of different species, and even varieties, cultivated on different medium, show great differentiation referring to metal intake. Harkot’s [5] study revealed that Lolium perenne could accumulate more copper than other species. The grass occurred in all tested grass mixtures at the amount of 20-35%.

Cadmium. Content of the element was obviously higher as a result of successive action of the sewage sludge. On average, 0.053 mg Cd·kg^-1 DM was found in plants in 2001 and 1.38 mg Cd·kg^-1 DM in 2002. Wołoszyk et al. [13] found different dependencies. Mixtures M1 and M3 collected in 2001 and M2 and Festulolium in pure sowing in 2002 contained the most cadmium. It seems that not only sewage sludge was the source of cadmium in the second year of study, but also the dumping ground itself, which is proved by content of the element in not treated plants.

Lead. In a case of lead, higher concentration was recorded in mixtures due to successive of sewage sludge than the direct action. Lead content in the second year was higher by 3 mg DM than in plants in the first year. Clear influence of sewage sludge rate on lead concentration in plants was observed in the second year. Its increase was proportional to sewage sludge doses. Wołoszyk et al. [13] achieved the same dependence. Mixture M1 and Festulolium in pure sowing accumulated slightly more lead in the first year and M4 and Festulolium in the second.

Nickel. The most nickel was determined in mixtures collected in the first year from control object. Grasses treated with sewage sludge contained significantly less nickel. The data point out to other than sewage sludge sources of nickel for plants. In the second year, higher by 2 mg Ni·kg^-1 DM was recorded in grass. No influence of sewage sludge rate on nickel concentration in tested mixtures was observed, because mean contents from all objects were similar. Wołoszyk and Krzywy [12], as well as Wołoszyk et al. [13] recorded different dependencies. In their studies, nickel concentration in grass mixtures increased along with the sewage sludge increase. In the first year, no mixture was distinguished referring to nickel level, and Festulolium contained the most nickel in the second year.

Cobalt. Its content in 2002 was 10-fold higher than in plants collected in 2001. In the first year, sewage sludge applied had not the influence on the element content. Plants from 2002, when higher sewage sludge rates were applied contained significantly more cobalt in relation to control and the lowest dose. Also no mixture was distinguished, because cobalt content in each one was similar in both years of study.

Heavy metal intake is presented in Tables 5 and 6. It is linear dependence of plant‘s weight vs. concentration of particular metals. Plants in the first year intook half of iron as in the second year of study. Amount of intake iron was higher in objects treated with sewage sludge than in control one. Particularly clear increase of intake occurred in objects with the lowest rate of sewage sludge. The level of iron intake by plants from objects treated with 40 and 60 kg was similar in both years of study. Intake level was not significantly dependent on type of mixtures applied. However, more iron was intake by plants of M1 and M3 mixtures in 2001, and M4 and M5 in 2002.

Accumulation of manganese in plants from 2002 was higher by about 100 mg than in those from 2001. No clear differences referring to the level of manganese intake by plants among objects treated with various sewage sludge doses were observed. Mixture M3 was distinguished in the first and M4 in the second year as referring to manganese accumulation.

Zinc intake was higher due to direct sewage sludge action than successive one. Quantity of intaken zinc in both years of study significantly depended on sewage sludge rate. However, its higher doses influenced similarly on the amount of intaken zinc by grasses. Plants of M3 mixture intook the most zinc in the first and these of M4 in the second year.

Level of copper intake by plants in the second year was 100-fold higher than in the second year. Plants from objects treated with higher rates of sewage sludge intook particularly much of the element. Mixtures M1 in the first and M4, M5 and Festulolium in the second year were distinguished referring to copper intake.

Plants intook more cadmium, lead, nickel and cobalt in the second as compared to the first year of study. The increase was 30, 8, 2 and 190-fold, relatively in relation to these components intake. Plants from objects with the lowest sewage sludge rate intook the highest amounts of these metals in relation to the control. Increasing the dose up to 60 kg did not significantly affect these metals intake by mixtures applied. Mixture M1 distinguished in the first, and M4, M5 and Festulolium in the second year of study.

The content of studied trace elements in dry mass of grass most influenced the amount of their intake. The grasses took much more trace elements in year 2002. The different intake in years was mainly due to a sampling date and course of climatic conditions. In the year 2001 the grass was mowed only one time, in september. In the year 2002, during increased bedding humidity (rainfall in may and june about 60mm), sampling was made in june. The increased mobilization of trace elements from sludges’ organic matter was occurred. It was shown mainly in content and intake of cadmium, cobalt and copper by plants.

CONCLUSIONS

Performed study points out to the possibility for utilization of sewage sludge to fertilize the no-soil cover of municipal dumping grounds. Then, in order to reduce the unfavorable influence of dumping grounds on the environment, it should be sodded. Therefore, proper grass mixtures that can develop under difficult conditions are searched for. Among applied mixtures, M4, M5 and Festulolium are the most suitable. They efficiently reduce the heavy metal migration within the environment. This type of study should be carried out for many years to univocally state which mixture would maintain under difficult conditions and it could be utilized in practice.

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