Iwa international Specialist Conference

¹L. Spinosa^, ²K. Wichmann & ³V. Lotito

¹Commissariat for Environmental Emergency, Bari (I)

²TUHH, Hamburg (D)

³CNR, Bari (I)
A number of requirements, such as guide and/or limit values, are contained in the european legislation on sludge, but methods for the determination of the respective parameters are often not available or described. For this reason, the European Committee for Standardization (CEN) established in 1993 the Technical Committee 308 (TC308) whose main scope is the standardisation of methods employed for sludge characterisation (Leschber and Spinosa, 1998).

Work is developed in three Working Groups, the first (WG1) dealing with the standardisation of methods for determining sludge parameters, the second (WG2) with the preparation of good practice guides for different use and disposal routes, and the third (WG3) with the preparation of documents on the current and future utilization and disposal of sludge in Europe.

Among the technological parameters more widely used for sludge characterisation (e.g. settleability, thickenability, specific resistance to filtration, compressibility, CST, etc.), the sludge "physical consistency", that is related to rheological properties, is of fundamental importance since this property strongly affects almost all treatment, utilisation and disposal operations, such as storage, pumping, transportation, handling, land-spreading, dewatering, drying, etc., which account up to 50% of the total costs for wastewater treatment.

Infact, in sludge land application, and storage and transportation steps, the selection of the most suitable equipment and procedure is strongly connected to the material consistency. Similarly, compacting sludge in a landfill or forming a pile in composting is depending on sludge shear strength rather than on its solids concentration (Spinosa and Lotito, 1999). Table 1 shows the importance of the sludge physical states in its management.

Table 1 - Importance of the sludge physical states in its management

(L=Low; M=Medium; H=High)

Operation	Liquid	Paste	Solid
Stabilisation	H	M	L
Dewatering	H	M/L	L
Storage/Transportation	H	H	H
Agricultural use	H	H	H
Landfilling	L	M/H	H
Incineration	L	M/H	H

Unlikely, standard methods for the evaluation of sludge consistency are not available yet, mainly due to the sticky nature of the sludge, which is strongly affected by its water content and water-solid bonding. To this purpose, the definition of the physical states of the sludge is preliminarly required, followed by the standardisation of measuring procedures able to give comparable and reliable results. These procedures must also be simple to be operated and applicable on the field.

The following three consistency cathegories have been proposed (Spinosa et al., 1999):

• 
  liquid, sludge flowing under the effect of gravity or low pressure;
  
• 
  paste-like, sludge capable of continuous flow under the effect of pressure above a certain treshold and having a shear resistance below a certain treshold;
  
• 
  solid, sludge having a high shear resistance.
  

It follows the need to develop laboratory procedures to define the boundary limit between liquid and paste-like behaviours (flowability) and that between solid and paste-like ones (solidity).

Considering that yield stress is a typical characteristic of non-newtonian fluids and that for a sludge the non-newtonian behaviour becomes more evident at higher solids concentration, the yield stress can be considered as indicator of sludge "flowability".

To this purpose, a simple equipment, i.e. a Kasumeter, consisting of a cylindrical container to which calibrated pipes of different diameters are fitted (Schulze et al., 1991) was used. Yield stress values were measured in terms of time necessary for the tested sludge to flow through a pipe of a certain diameter, and then compared to those obtained through a conventional rotating viscometer.

Tests were run by using synthetic suspensions of kaolin and quartzsand in water at different solids concentrations, to avoid problems connected to the complex and changing nature of real sludges, and municipal sewage sludges at different solids concentrations obtained through dilution of dewatered sludge by means of filtrate.

Results showed that yield stress values calculated by the Kasumeter apparatus can be well correlated to those obtained by a conventional rotating viscometer, thus allowing the limit of flowability to be evaluated in a very simple way.

As far as the "solidity" limit is concerned, several apparatuses for measuring mechanical properties (i.e. a laboratory vane shear, a pocket vane shear, and a pocket cone penetrometer) were investigated for the evaluation of the shear strength of different waterworks sludges.

Tests showed that the laboratory vane shear apparatus could be possibly taken as reference device, while the pocket penetrometer could be more useful in the field, expecially because of good handling (Wichmann and Riehl, 1997).

Further, the comparison of values measured, by a Vicat needle instrument, as a function of penetration into the sludge of needles of different shape and size, to those obtained through a conventional vane shear apparatus and a cone penetrometer, showed that the Vicat needle could possibly be a good instrument to measure the solidity limit.

References

Leschber R. and Spinosa L. (1998). Developments in sludge characterization in Europe. Water Science and Technology, 38, 2, 1-7.

Schulze von B., Brauns J. and Schwalm I. (1991). Neuartiges baustellen-meβgerät zur bestimmung der flieβgrenze von suspensionen. Geotechnik, 14, 125-131.

Spinosa L. and Lotito V. (1999). Rheological measurements and their application in biosolids management. Water21, Sept.-Oct., 28-29.

Spinosa L., Remy M. and Wichman K. (1999). Physical consistency - Measurement of sludge consistency. CEN/TC308/WG1/TG3 Report R1.

Wichmann K. and Riehl A. (1997). Mechanical properties of waterwork sludges - Shear strength. Water Science and Technology, 36, 11, 43-50.

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BIOSOLIDS 2003 – Wastewater Sludge as a Resource
ABSTRACT
Heavy metals in sludge – relationship between wastewater and sludge
R.Storhaug
Aquateam – Norwegian Water Technology Centre, Oslo

The heavy metal content in sewage sludge is one of the most important factors affecting the final sludge disposal. Concequently the Norwegian regulation on sewage sludge treatment and disposal includes maximum values for heavy metal concentration (Cd,Hg,Pb,Cr,Ni,Zn,Cu) in sludge for disposal in agriculture or on green areas.

During the last 20 years there has been a constant decline in the heavy metal concentration in the sludge. Table 1 shows the average heavy metal concentration in Norwegian sewage sludge from 1980 to 2000.
Table 1 Average heavy metal concentration in Norwegian sewage sludge 1980 - 2000

Year Metal	Heavy metal concentration (mg Me/kg DS)
	1980	1991	1996	2000	Maximum content ^1)
					Use in agriculture	Use on green areas
Cd	4,0	1,7	1,0	1,0	2	5
Hg	12	2,1	1,2	0,9	3	5
Pb	118	36	24	21	80	200
Ni	42	12	11	15	50	80
Cr	233	30	28	25	100	150
Zn	687	376	352	317	800	1500
Cu	474	399	256	244	650	1000

1. 
   Norwegian regulation on sewage sludge
   

The improved quality of the sludge is mainly caused by more stringent regulations put on the industrial discharges to the municipal sewerage system, and general ban of specific heavy metals, e.g. cadmium.

However, the sludge quality at some plants do not meet the regulations for heavy metal content for a shorter or longer period of time. The main reason is point source discharges. The most important activities causing problems for the sludge quality are:

• 
  Wastewater from off-gas treatment at solid waste incineration facilities (cadmium)
  
• 
  Wastewater from small metal-plating industries (zinc, chromium)
  
• 
  Wastewater from airports , different activities as cleaning and maintenance of the aircrafts (cadmium)
  
• 
  Discharges from dental clinics (mercury)
  
• 
  Discharges from small industrial activities with insufficient internal control system causing discharge of untreated wash water or disposal of low quality products
  
• 
  Wastewater from car wash facilities (cadmium)
  
• 
  Wastewater from analytical laboratories
  

The main focus has been put on the heavy metal concentration in sludge, and to a less extent to the heavy metal concentration in the incoming wastewater to the treatment plants. The heavy metal concentration in the influent water is normally analysed on larger wastewater treatment plants (>50.000 PE). To obtain a more efficient early warning system to avoid incidents with high heavy metal concentrations in the sludge, there is a need to focus on the daily transport of heavy metals into the treatment plants. From a normal transport of heavy metals (e.g. g Cd/day) establish alarm limits that causes action plans to be put in operation whenever the limits are exceeded.

The paper will present results from monitoring the heavy metal concentration in the incoming wastewater and the resulting heavy metals concentration in the sludge. Methods for a systematic search for heavy metal point sources including use of passive samplers will also be presented.
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Bacterial composition of activated sludges – importance for floc and sludge properties
Per H. Nielsen, Jeppe L. Nielsen, and Trine R. Thomsen

Aalborg University, Department of Environmental Engineering, Sohngaardsholmsvej 57, DK-9000 Aalborg, Denmark

ABSTRACT

Activated sludge flocs consist of numerous constituents, such as bacteria, EPS, organic and inorganic particles. These constituents are together with other factors, e.g. the physical conditions, responsible for the floc structure and the floc properties. These properties, on the other hand, largely determine the sludge properties, such as flocculation, settling and dewaterability.

When we want to assess the direct role of the bacteria on floc and sludge properties several questions appear: What is the amount of bacteria in the floc (of all organic matter), how many are alive and active, what kind of bacteria are present in terms of function and taxonomic affiliation, which factors determine the in bacterial composition in different treatment plants, how does different species affect floc and sludge properties and how can microbial activities affect the properties. Answers to these and several other questions are important if we want to understand the behavior of activated sludge flocs, and if we want to control and optimize sludge properties.
In this paper we will briefly review the present knowlegde about the role of bacteria on floc and sludge properties, and we will present a new approach to investigate the identity and the function of the bacteria present in the activated sludge flocs.

The approach includes an identification of the important bacteria and a characterization of their physiological and functional properties directly linked to the different bacterial species. The identification and quantify the different bacteria directly in the sludge flocs are carried out by use of culture independent molecular biological methods, e.g. fluorescence in situ hybridization, FISH (Daims et al., 2001; Nielsen et al., 2002a). The physiology can be studied by use of radiolabelled substrates (microautoradiography, MAR, Nielsen and Nielsen, 2002a,b) or various types of fluorescent probes (Nielsen et al., 2002b).

Using this approach is has been found that poor and good settling flocs in a certain treatment plant are different in size and physical structure and – very important in this context - they are also composed of different bacterial populations (Schmid et al., 2002). Thus, all flocs do not have an identical microbial composition within the same plant, which is important for our understanding about an “average” sludge floc. Likewise, we here present the results of an investigation of the shear sensitivity of the different bacterial species forming microcolonies within flocs from different activated sludge treatment plants. We could clearly show that different microcolony-forming bacteria had a different sensitivity to shear. In particular, bacteria belonging to the Alphaproteobacteria, Bacteroides and Firmicutes were very sensitive, while most microcolonies belonging to the Betaproteobacteria were hardly affected by the shear applied. Furthermore, the shear sensitivities of the sludges investigated differed in a way that reflected the variations in the bacterial population composition.
In conclusion, the approach to combine identity with functional analysis of the dominant bacteria in activated sludge by in situ methods is in our opinion a very promising way to investigate correlations between presence of specific bacteria and floc and sludge properties of interest. The perspectives will be discussed in the paper.

References

Daims, H., J.L. Nielsen, P.H. Nielsen, K.-H.Schleifer, and M. Wagner (2001). In situ characterization of Nitrospira-like nitrite-oxidizing bacteria active in wastewater treatment plants. Appl. Environ. Microbiol. 67(11): 5273-5284.

Nielsen, J.L. and P.H. Nielsen (2002a) Quantification of functional groups in activated sludge by microautoradiography. Wat. Sci. Tech. 46(1-2): 389-395.

Nielsen, J.L. and P.H. Nielsen (2002b): Enumeration of acetate-consuming bacteria by microautoradiography under oxygen- and nitrate respiring conditions in activated sludge. Wat. Res. 36: 421-428.

Nielsen, J.L., Juretschko, S., Wagner, M. and Nielsen, P.H. (2002a) Abundance and phylogenetic affiliation of iron reducers in activated sludge as assessed by fluorescence in situ hybridization and microautoradiography. Appl. Environ. Microbiol. 68(9): 4629-4636.
Nielsen, P.H., P. Roslev, T. Dueholm and J.L. Nielsen (2002b) Microthrix parvicella, a specialized lipid consumer in anaerobic – aerobic activated sludge plants Wat. Sci. Tech 46(1-2): 73-80.

Schmid, M, A. Thill, U. Purkhold, M. Walcher, J. Y. Bottero, P. Ginestet, P. H. Nielsen, S. Wuertz and M. Wagner (2002). Characterization of activated sludge flocs by confocal laser scanning microscopy and image analysis. Wat. Res. (accepted)

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