The influence of the waste water sediments on soils' agrochemical indicators

In modern conditions technogenic influence became one of powerful factors of environment pollution. The violation of requirements at storage of the waste waters sediments as its uncontrolled use as fertilizers represents great danger for soils and agricultural production.

The main enterprises - producers of the waste waters sediments in the territory of the Orel region are Municipal unitary manufacturing enterprise of water and sewer utilities «Orelvodokanal» with a volume of dumping of sewage of 52 925 thousand m3/year, Vodokanal Municipal Unitary Enterprise in the cityLivni – 3 17,7 thousand m3/year, Vodokanal Municipal Unitary Enterprise in the city Mtsensk – 6702,650 thousand m3/year. Besides, about 250 treatment facilities of mechanical and biological cleaning are in the territory of the region. The vast majority of them has the big lifetime, doesn't meet the modern requirements of ecological safety, doesn't provide due sewage treatment. The treatment facilities are absent in many regional centers at all.

The waste waters of Orel city are one of the main waste of household and practical activity of the population in the city. About 30 kg of dry sediment of sewage are annually made for one resident. The total of mechanically dewatered sediment made in a year on the treatment facilities of the city sewerage served by Municipal unitary manufacturing enterprise of water and sewer utilities «Orelvodokanal» makes 54750 tons per 80% of humidity. The bulk of sediments take place on storage platforms which are located in «Orelvodokanal» territory. The part of the waste waters sediments is placed in the of lands of an near-by territory agricultural purpose: on two sites of 345, 34 sq. m and 3934, 57 sq. m that led to overlapping of a fertile soil layer, that is to lands damage.

This group of waste is continuously formed, processed and often takes place in territory of treatment facilities which settle down in city line or near lands of agricultural production. Constant accumulation of waste in the territory of treatment facilities can constitute a serious ecological threat.

The chemical composition of the waste waters sediments, depending on arriving on treatment facilities industrial and municipal drains, and also definition methods and fluctuates in rather wide range. The waste waters sediments are characterized by a wide set macro -and microelements, including as well heavy metals. The waste waters sediments contain 1,01,34% of the general nitrogen, 0,21-0,23% of the general phosphorus, 0,32-0,36% of the general potassium at рН – 4,8-5,0.

High humidity, difficulty of removal from sludge banks, insufficient quantity and imperfection of mechanisms and vehicles for cleaning of sediments, availability of salts of heavy metals in them and pathogenic microflora are the reasons which restrain the use of sediments.

MATERIALS AND METHODS OF RESEARCH

The work purpose is to establish the influence of production wastes in the form of the waste waters sediments on environment and agroecological indicators of the soil.

Researches were conducted on sites of overlapping of top soil of Municipal unitary manufacturing enterprise of water and sewer utilities «Orelvodokanal» which is located not far from village Vjazki in the Orel region. These are the lands of agricultural purpose with a total area of 4280 sq.m.

The techniques accepted in experiments on plant growing, agriculture, soil science and agrochemistry were used in researches:

• a)    The maintenance of humus in the soil – by Tyurin;

• b)    рН salt extract – by potentiometric method;

• c)    Hydrolytic acidity – by Kappena;

• d)    The sum of the exchange bases – by Kappenu-Gilkovitsu;

• e)    Mobile: phosphorus (P 2 O 5 ) and potassium (K 2 O) – by Chirikov;

• e)    The general nitrogen – by Kjeldal;

• g)    Nitrogen– by Kornfild.

The specified methods are described in manuals and practical works: «Agrochemical methods of research of soils» (1965); «Workshop on soil science» (I.S. Kaurichev, 1973); «Guide to the chemical analysis of soils» (E.V. Arinushkina, 1970); «Workshop on agrochemistry» (L.V. Peterburgsky, 1968; A.S. Radov, etc., 1985; B. A. Yagodin, etc., 1987).

Soil researches were conducted on previously selected samples according to existing regulations in the field of the soil analysis and sampling methods. The soil cover of a studied site is presented by gray forest soils of loamy mechanical structure.

RESULTS AND DISCUSSION

During the researches stocks of nutrients in the soil, their distribution on a profile, an existential variation in the soil and availability to plants were considered. Indicators: soil acidity, accessible forms of nitrogen, phosphorus, potassium, microelements, environment reaction, the maintenance of the absorbed bases and humus.

• 10 soil samples from a site of overlapping of a fertile layer and 3 tests from the territory adjacent to treatment facilities are investigated (control). The results of researches of the soil samples are given in table 1.

Due to acidity degree soils are subdivided into highly acidic, having pH 3,5-4.0; the sour - 4.0-5.0; the subacidic - 5.0-6.0; the neutral - 7.0; the alkaline - 7.0-8.0; the highly alkaline- 8.0-8.5.

Table 1 - Results of laboratory researches of soil samples

Test number	Agrochemical indicators, mg/kg
	humus, %	Phosphorus, (P2O5)	Potassium (K2O)	Nitrate nitrogen	рН, unit
The tests which have been selected on a site of overlapping of a soil fertile layer
1	3,15	327,2	367,7	301,0	5,59
2	0,51	119,3	183,0	107,9	7,41
3	2,74	233,0	85,6	145,1	7,0
4	1,32	149,8	101,5	163,8	6,69
5	2,63	231,4	178,2	290,3	7,03
6	1,46	157,6	152,0	139,7	6,85
7	0,81	102,0	69.7	413,4	6,62
8	2,56	218,6	247,4	197,0	6,32
9	1,98	190,0	143,0	218,7	6,67
10	0,59	196,7	104,3	158,5	7,07
average	1,78	192,6	163,2	213,5	6,73
The control tests which have been selected in the near-b				territory
1	2,53	211,2	183,6	110,6	7,0
2	2,56	214,1	219,3	90,7	6,97
3	2,66	238,5	259,4	60,6	6,83
average	2,58	221,3	220,7	87,3	6,93
Tests to control	- 0,803	- 23,0	- 57,5	+ 126,2	+ 0,2
	31,1%	14,3%	26,1%	244,5%	2,9%

Soils acidity in the selected samples on a site of overlapping of a non-uniform layer of the waste waters sediments varies from neutral (pH 6,32-6,85) to alkaline (pH 7,0-7,41) at average value 6,73 that is 2,9% higher, than at a control sample (pH 6,93). It means that the waste waters sediments have acidifying effect on a soil fertile layer and accumulation of toxic for plants of mobile aluminum in it.

The maintenance of humus in the soil (the content of organic substance) is the main agroecological indicator. The humus is a source of the most part of nitrogen available to plants. At its mineralization there is also a phosphorus release.

According to the maintenance of a humus the soils are considered to be very poor as its 1% at the contents and less, the poor 1-2%, insufficiently provided 2-3%, moderately provided 3-4%, well provided - more than 5%.

The maintenance of a humus in the selected samples on a site of overlapping of a soil fertile layer of the waste waters sediments varies from 0,51% (the poorest soils) to 3,15% (average income) at average value of 1,78% (poor) that is 31,1% less, than the contents it in a control sample (2,58). It means that at this conjuncture the waste waters sediments reduce the content of organic substance in the soil that leads to deterioration of soil fertility.

Degree of providing with soils by mobile forms of phosphorus (P2O) is estimated by the following indicators, mg/kg: the soil to 30,0 - very low; 31,0-80,0 - the low; 81,0-150,0 -average; 151,0-200,0 - the raised; 201,0- 300,0 - the high; more than 300 - very high.

The maintenance of mobile forms of phosphorus in the selected samples on a site of overlapping of a fertile layer varies from 102, 0 mg/kg of the soil (average) to 327,2 mg/kg of the soil (high) at average value of 192,6 mg/kg of the soil (raised) that is 14,3% less, than at a control sample (221,3 mg/kg of the soil). It means that the waste waters sediments lowered the maintenance of mobile forms of phosphorus on a studied site.

Degree of providing with soils by mobile forms of potassium (K20) is estimated by the following indicators, soil mg/kg: to 40,0 - very low; 41,0-80,0 - the low; 81,0-140,0 - average; 141,0-200,0 - the raised; 201,0-300,0 - the high; more than 300 - very high.

The content of mobile forms of potassium in the selected samples on a site of overlapping of fertile soil layer of the waste waters sediments varies from 69,7 mg/kg of the soil (low) to 367,7 mg/kg of the soil (very high) at average value of 163,24 mg/kg of the soil (raised) that is 26,1% less, than at a control sample (220,7 mg/kg of the soil). It testifies that the waste waters sediments reduce the content of potassium mobile forms.

The analysis of these laboratory researches of the soil samples which have been selected on a studied site of disturbed lands (tab. 1), shows the high content of nitrates with maximum residue limit excess (130 mg/kg). Maximum residue limit excess of nitrates varies from 139,7 mg/kg to 244,5 mg/kg at average value 213,5 mg/kg that is 144,5% higher, than at a control sample (87,3 mg/kg of the soil).

Thus, in the conditions of studied object overlapping and a fertile layer of waste waters sediments leads to accumulation of nitrates in a fertile soil layer and, finally, in crop production.

CONCLUSIONS

The decrease of a humus content for 31,1%, mobile forms of phosphorus for 14,3%, potassium for 26,1% is revealed on a site of overlapping of a fertile layer by the waste waters sediments and soils acidity increases by 2,9% in comparison with control.

The waste waters sediments storage on a studied site led to sharp accumulation of nitrates in the soil, with maximum residue limit excess from 18,2% (Ave. No. 6) to 218,0% (Ave. No. 7), at an average value for 244,5%.

It is required to carry out a complex of the actions directed on restoration of lost natural fertility of soils for elimination of negative impact of waste waters sediments on environment and soil fertility on a studied site.