Sludge Wastewater Treatment Plant Research Articles

Deep dewatering of activated sludge using composite conditioners of surfactant, acid and flocculant: The mechanism and dosage model

To address the problem of difficult disposal caused by poor dewaterability of high-organic sludge in wastewater treatment plant, this study developed a sludge composite conditioner (SCC) consisting of sodium dodecyl sulfate (SDS), HCl and FeCl3. It has the potential to significantly improve the dewaterability of the high-organic sludge with the VSS/MLSS of 80%. The moisture content (MC) and bound water content of sludge were reduced from 98.00 to 59.65% and from 3.42 to 0.91 g/g dry sludge (DS) after being conditioned, respectively. The surfactant (SDS) promoted the dissolution of extracellular polymeric substances (EPS). The acid (HCl) enhanced the decomposition of the sludge flocs, making the insoluble EPS peel off and turn into the liquid phase. As a result, total EPS decreased by 52.70% compared to the original sludge. In addition, due to the neutralization effect of protons and FeCl3, the Zeta potential increased remarkably from −13.80 mV to −1.72 mV and the dispersed sludge particles formed during EPS dissolution process were re-flocculated, which increased the average size of the sludge particles. The ratio of proteins (PN)/polysaccharides (PS) also increased from 1.69 to 3.81. And a quantitative model of optimum dosage of SCC agents based on the influence of the sludge PS, PN and EPS content has been established, aiming to determine the dosage of each conditioner according to the properties of target sludge. In general, the SCC provided an effective pathway for sludge deep dewatering.

Meta-analysis of Microbial Communities in the Activated Sludge of Wastewater Treatment Plants Under Different Climate Types

Microbial communities in wastewater treatment plants(WWTPs) are very important for water purification in the context of public drinking water safety and environmental health. Therefore, it is necessary to explore the trends in microbial community structure and diversity in sewage treatment plants and their main environmental impact factors under different climates in China. Based on high-throughput sequencing techniques, a meta-analysis was conducted to screen the 16S rRNA genes in an open database. We analyzed the trends in microbial community structure and diversity in WWTPs under three climate types(Dwa, Cfa, and Cwa) in China. We then constructed cohesion models to examine the core microbial taxa and their interactions within the communities. We also used a piecewise structural equation model(PSEM) to examine the effects of different climate types on microbial community structure. The three climate types significantly affected the structure and diversity of the microbial communities, with patterns correlated with influent pH, mixed liquid temperature, conductivity, and nitrogen concentrations(P<0.05). Based on the PSEM analysis, the β-diversity of the microbial communities was directly correlated with latitude, while α-diversity was indirectly correlated with latitude through conductivity and water temperature. Based on the cohesion modeling, microbial community stability was the highest under Dwa climate followed by the Cfa climate. This could be explained by a small subset of highly connected taxa capable of withstanding disturbance, indicating an important stability role. In contrast, the stability of the microbial communities under the Cwa climate was low, and no species with strong negative cohesion were observed. Overall, the structure, diversity, and stability of microbial community in WWTPs were found to be sensitive to climate, and the responsive mechanisms of α-diversity and β-diversity with respect to latitude were distinct.

Speciation and Ecological Risk Assessment of Heavy Metal(loid)s in the Municipal Sewage Sludge of China

To reveal the speciation and pollution status of heavy metal(loid) s (HMs) in the dewatered sewage sludge(SS) of municipal wastewater treatment plants(MWTPs) in China, SS samples were collected from 40 MWTPs located in different regions of China. The total concentrations and geochemical fractions of As, Cd, Cr, Cu, Ni, Pb, and Zn in the SS samples were analyzed. The ecological risks induced by HMs in the SS were assessed based on the toxicity characteristic leaching procedure(TCLP), risk assessment code(RAC), and potential ecological risk index(RI). The median values of HMs in SS followed the order Zn > Cu > Cr > Pb > Ni > As > Cd. The general attainment rates of HMs in SS were satisfactory(>90%). As showed a generally even distribution among all the fractions; Cd and Zn mainly existed in the reducible fraction; Cr mainly occurred in the residual fraction, followed by oxidizable and reducible fractions; Cu mainly occurred in the oxidizable fraction; Ni occurred mainly as exchangeable forms; and Pb mainly occurred in the reducible and residual fractions, with its exchangeable form being the lowest fraction. According to the RAC method, the environmental risks induced by HMs in the SS followed the order Ni > As > Zn > Cd > Cu > Cr > Pb. The ecological risk of Ni was high; Zn, As, and Cd had a medium level of risk; Cr and Cu had a low level of risk; and the risk of Pb was negligible. According to the RI method, Cd and Cu showed the highest potential ecological risk, indicating that these are the primary HM pollutants in the SS. However, if the agricultural application of SS is carried out in accordance with the national standards, the overall level of risk from soil HM pollution is considered relatively low.

Evaluation of Land Potential for Use of Biosolids in the Coastal Mediterranean Karst Region

The aim of this study was to evaluate the potential of agricultural land in the coastal Adriatic Karst region (Šibenik region, Croatia) for biosolids application by integrating spatial data from different sources: digital maps and remote sensing, parcel identification system, GIS field observations and measurements focusing on specific land and soil properties. Due to the rapid development of the wastewater treatment industry, excessive accumulation of sewage sludge (SS) in wastewater treatment plants is a growing problem worldwide. Management options for land application of biosolids require a comprehensive characterization of both SS and SS-amended soils. The assessment of agricultural land in the study area for SS disposal was based on EU and national legislation. The evaluation revealed that agricultural land in the study area accounts for only 10% of the total area (25,736 ha), but only a quarter of the existing land (6065 ha) is suitable for biosolids application. Furthermore, the data indicate that the sewage sludge can be safely applied to the soil in terms of soil metals according to the Croatian legislation. The short-term potential of the soil to sustain this ecosystem service, namely soil improvement with biosolids, should be used to determine the inherent long-term potential based on resistance to soil degradation and resilience. However, caution is needed and the long-term effects should be investigated before biosolids are continuously used for soil application.

Investigation of microplastics in sludge from five wastewater treatment plants in Nanjing, China

Municipal wastewater treatment plants (WWTPs) have been regarded as the main receptors of microplastics in industrial and domestic wastewater. The excess sludge they generate is an important carrier for the microplastics to enter the environment. In China, relevant regional studies are still in an initial phase. In this work, microplastics in the sewage sludges at different sampling points of five WWTPs in Nanjing City (an important city in the Yangtze River basin) were investigated, including their abundance, morphology and chemical composition. Furthermore, the influence factors such as population density, economic development level, wastewater source and treatment process were also discussed. The analysis results through optical microscope and FT-IR showed that the detected microplastics were divided into fragments, films, fibers and granules. Their chemical component reached up to 19 species, including small amounts of petroleum resins which was scarcely detected in other studies. Wastewater source was the primary factor influencing the microplastic abundance and size in sludge. And the microplastic shape and chemical components were closely related to the industrial type. Furthermore, because the removal effect on the microplastics with different morphologies were varied with the treatment process, the preliminary suggestions on the technology for particular wastewater were proposed. This study provides partial regional data and analysis for the microplastics contained in the sludge of WWTPs, expecting to provide a certain theoretical support for the operations management of WWTPs and standardized sludge treatment.

Nitrosation and nitration of diclofenac and structurally related nonsteroidal anti-inflammatory drugs (NSAIDs) in nitrifying activated sludge

Diclofenac (DCF) is a highly consumed non-steroidal anti-inflammatory drug that is excreted partially metabolized and is poorly removed during wastewater treatment. Previous findings demonstrated that DCF in wastewater treatment plants (WWTP) is partially removed to nitro/nitroso compounds. The reactive nitrogen species, that are microbially produced during nitrification in the activated sludge of WWTP, were suspected to be involved in the transformation of DCF. Therefore, here, we investigated the molecular features governing such biotransformation and the role played by nitrifying bacteria by biodegradation experiments at lab scale in enriched nitrifying sludge bioreactors spiked with DCF and other structurally related non-steroidal anti-inflammatory drugs (NSAIDs). We provided evidence of the incorporation of NO/NO2 groups into DCF originated from ammonia by isotopically labelled biodegradation experiments. Nitroso and nitro-derivatives were tentatively identified for all NSAIDs studied and biotransformation mechanisms were proposed. Our findings from biodegradation experiments performed under different incubation conditions suggested that biotransformation of DCF and its related NSAIDs might not only be microbially mediated by ammonia oxidizing bacteria, but other nitrifiers co-occurring in the activated sludge as ammonia oxidizing archaea and nitrite oxidizing bacteria. Follow-up studies should be conducted to disentangle such complex behaviour in order to improve removal of these contaminants in WWTPs.

Distribution of microplastics in the sludge of wastewater treatment plants in chengdu, China

Large amounts of microplastics can accumulate in wastewater treatment plants (WWTPs), and sludge disposal is suspected to be a major source of microplastics pollution in the environment. It is therefore important to investigate the distribution of microplastics in the sludge of each processing unit of WWTPs. However, little information is available on this topic in China. Accordingly, in this study, the abundance and characteristics of microplastics in the sludge of two WWTPs in Chengdu were investigated. The abundance of microplastics in the sludge samples ranged from 44.4 n·kg−1 to 750.0 n·kg−1. Microplastics were mainly divided into particles (32.16%), debris (28.14%) and fibers (17.08%) according to their shape, and the colors of the microplastics were mainly green (35.19%) and translucent (18.06%). The particle sizes were mainly larger than 1 mm in dimension. Polyethylene, polypropylene and polystyrene were the prevalent types of microplastics analyzed. Our results provide basic information for better understanding the characteristics of microplastics in sludge and for improving sludge treatment.

Phosphorus recycling from activated sludge of full-scale wastewater treatment plants by fast inversion of the biological phosphorus elimination mechanism

Enhanced biological phosphorus removal (EBPR) is often applied by wastewater treatment plants (WWTPs) whereby phosphorus (P) is accumulated in the activated sludge (AS) biomass. The German Sewage Sludge Ordinance demands that large WWTPs recycle P from their process streams by 2029. This study aimed at evaluating the potential of an acetate-mediated P re-dissolution from non-acclimated AS of three full-scale WWTPs. All AS exhibited enhanced P re-dissolution during acetate uptake and followed kinetics typical of EBPR systems. Re-dissolution efficiency differed depending on the WWTP operation mode. The highest P re-dissolution yield (56% of total P) was obtained for pure EBPR sludge. Lower re-dissolution rates of 19–22% were observed in the AS from WWTPs that employed additional chemical P removal, probably due to shortage of intracellular polyphosphate. Pure EBPR systems may be suited for the implementation of a re-dissolution based strategy for P recycling from AS where P depleted AS could potentially be returned to the biological treatment stage.

Evaluation of the biogas potential of a lignocellulosic residue.

Anaerobic digestion (AD) or methanization is a biological process that allows the treatment of organic wastes and the production of renewable energy as biogas. This research describes assessment and optimization of dates pedicels rich in organic components under the conditions of mesophiles in co-digestion in association with the cattle manure and sludge of the wastewater treatment plant (WWTP). To realize this objectives, we investigated the impact of substrate load (date pedicel) on the co-digestion anaerobic of date pedicels and the sludge in wastewater treatment plants. The different parameters of the digester stability such as the pH, VFA, CAT, ammoniacal nitrogen, and the volume of biogas produced were followed. The results show that by increasing the mass of the pedicels and therefore the percentage of the substrate in the reactor, from 0.5 to 1% (W/V), the volume of produced biogas increases by five times. However, an increase in the percentage of the substrate introduced into the digester from 1 to 2% resulted in a slight decrease in the volume of biogas produced. The use of fresh cattle manure as inoculum shown a significant improvement (40%) in the production of biogas, which can be attributed to the nature of the inoculum. Indeed, cattle manure fresh is more adapted for the fermentation of lignocellulosic materials unlike sludge of wastewater treatment plants which may contain toxic substances that limit their use in AD.

Regulation of anaerobic fermentation for producing short-chain fatty acids from primary sludge in WWTPs by different alkalis

Carbon source production from primary sludge in wastewater treatment plants (WWTPs) via anaerobic fermentation process has been paid more attention. However, slow hydrolysis rate and low yield of short-chain fatty acids (SCFAs) limited its application. This study aimed at improving the anaerobic fermentation efficiency of primary sludge by alkali regulation (NaOH, Na2CO3 and Ca(OH)2), and revealing the mechanism. Results showed that three kinds of alkalis allowed enhancing hydrolysis and acidification, and reducing methane production in the anaerobic fermentation process of primary sludge. The Na2CO3 regulation contributed to highest yield and productivity of SCFAs, reaching 1626 mg COD/L and 0.189 g COD/g VSS at 4th day, respectively. Microbial community structure analysis indicated that the relative abundance of fermentative microbial community was improved in the alkali regulation system, where methanogenic archaea was effectively inhibited. The continuous flow experiment further verified that the Na2CO3 regulation could steadily increase yield of SCFAs in the anaerobic fermentation process of primary sludge, and the yield was also the highest among three kinds of alkali regulation.

Evaluation of estrogenic and antiestrogenic activity in sludge and explanation of individual compound contributions

Mixture toxicity, including agonistic and antagonistic effects, is an unrevealed environmental problem. Estrogenic endocrine disruptors are known to cause adverse effects for aquatic biota, but causative chemicals and their contributions to the total activity in sewage sludge remain unknown. Therefore, advanced analytical methods, a yeast bioassay and mixture toxicity models were concurrently applied for the characterization of 8 selected sludges with delectable estrogenic activity (and 3 sludges with no activity as blanks) out of 25 samples from wastewater treatment plants (WWTPs). The first applied full logistic model adequately explained total activity by considering the concentrations of the monitored compounds. The results showed that the activity was primarily caused by natural estrogens in municipal WWTP sludge. Nevertheless, activity in a sample originating from a car-wash facility was dominantly caused by partial agonists – nonylphenols – and only a model enabling prediction of all dose-response curve parameters of the final mixture curve explained these results. Antiestrogenic effects were negligible, and effect-directed analysis identified the causative chemicals.

Enhancing Phosphorus Recovery and Dewaterability of Waste Activated Sludge for Combined Effect of Thermally Activated Peroxydisulfate and Struvite Precipitation

Phosphorus is a nonrenewable and irreplaceable limited resource, and over 90% of phosphorus in influenttransfers into sludge in wastewater treatment plants. In this study, thermally activated peroxydisulfate (TAP) treatment was combined with struvite precipitation to enhance waste activated sludge (WAS) dewaterability and phosphorus recovery. TAP simultaneously enhanced dewaterability and solubilization of WAS. The optimal conditions of TAP treatment were PDS dosage 2.0 mmol/g TSS, 80 °C, pH 4.0~7.0 and 40 min, which enhanced dewaterability (capillary suction time (CST) from 94.2 s to 28.5 s) and solubilization (PO43−-P 177.71 mg/L, NH4+-N 287.22 mg/L and SCOD 10754 mg/L). Radical oxidation disintegrated tightly bound extracellular polymeric substances (TB-EPS) and further released bound water. The acidification effect neutralized the negative surface charge of colloid particles. Compared with thermal hydrolysis, TAP effectively promoted the release of PO43−, NH4+ and SCOD. Cation exchange removed most Ca and Al of the TAP treated supernatant. The optimal conditions of struvite precipitation were Mg/P 1.4 and pH 10.0, which achieved phosphorus recovery of 95.06% and struvite purity of 94.94%. The income obtained by struvite adequately covers the cost of struvite precipitation and the cost of WAS treatment is acceptable.

Comparison of different pretreatment methods on phosphorus release and recovery as struvite from excess sludge

ABSTRACT Recovering phosphorus (P) from excess sludge of wastewater treatment plants (WWTPs) has attracted considerable attention. An efficient P release method is undoubtedly critical for a satisfactory recovery performance. In this study, the effectiveness of three sludge pretreatment methods, i.e. anaerobic digestion (AD), EDTA-anaerobic digestion (EA) and ultrasound combined with EA (U-EA), on P release and struvite recovery from excess sludge was investigated. The results showed that different pretreatment methods resulted in the different characteristics of P release and recovery. For P release, the highest P release rate (57.14% of sludge total phosphorus, TP) was achieved by U-EA pretreatment, followed by EA and AD. Furthermore, U-EA was beneficial for sludge disintegration and reduction, by which the mixed liquor suspended solids (MLVSS) reduction rate reached 42.00% at a specific energy of 110,000 kJ/kg TS. For the P recovery (in the form of struvite), there was only a little difference in the optimal conditions and P recovery rate (89.29–94.49% of TP in the supernatant). AD pretreatment was beneficial for the purity of products and achieved the highest struvite purity (85.14%), followed by EA (80.95%) and U-EA (77.56%). In summary, the highest recovery rate of TP from excess sludge (53.50% of sludge TP) and struvite yield (26.10 mg/gSS) was obtained by U-EA.

Denitrification Process Enhancement and Diversity of the Denitrifying Community in the Full Scale Activated Sludge System after Adaptation to Fusel Oil

Implementation of anaerobic digestion of primary sludge in modern wastewater treatment plants (WWTPs) limits the availability of organic carbon for denitrification in conventional nitrification-denitrification (N/DN) systems. In order to ensure efficient denitrification, dosage of the external carbon source is commonly undertaken. However, application of commercial products, such us ethanol or acetate, greatly increases operational costs. As such, inexpensive and efficient alternative carbon sources are strongly desirable. In this study, the use of the fusel oil, a by-product from the distillery industry, was validated in terms of the denitrification process enhancement and impact on the activated sludge bacterial community structure. The experiment was conducted at a full scale biological nutrient removal facility (210,000 PE), in the set of the two technological lines: the experimental line (where fusel oil was introduced at 45 cm3/m3 dose) and the reference line (without an external carbon source addition). During the experimental period of 98 days, conventional nitrate utilization rate (NUR) measurements were carried out on a regular basis in order to assess the biomass adaptation to the fusel oil addition and denitrification process enhancement. While the NURs remained at a stable level in the reference line (1.4 ± 0.1 mg NO3-N/g VSS·h) throughout the entire duration of the experiment, the addition of fusel oil gradually enhanced the denitrification process rate up to 2.7 mg NO3-N/g VSS·h. Moreover, fusel oil contributed to the mitigation of the variability of NO3-N concentrations in the effluent from the anoxic zone. The bacterial community structure, characterized by 16S rRNA PCR—DGGE and the clone libraries of the genes involved in the denitrification process (nirS and nirK), was comparable between the reference and the experimental line during the entire experimental period. In both analyzed lines, the most frequent occurrence of denitrifiers belonging to the genera Acidovorax, Alcaligenes, Azoarcus, Paracoccus and Thauera was noticed. Our results proved that fusel oil would a valuable substrate for denitrification. The addition of fusel oil enhances the process rate and does not reflect a severe selection pressure on the bacterial community at applicable doses. Practical application of fusel oil generates opportunities for the WWTPs to meet effluent standards and reduce operational costs, as well as optimizing waste management for the distillery industry.

Macroinvertebrate interactions stimulate decomposition in WWTP effluent-impacted aquatic ecosystems

Aquatic ecosystems worldwide are impacted by an influx of nutrients and sludge particles from wastewater treatment plant (WWTP) effluents, leading to a degradation of benthic habitats and a loss of associated macroinvertebrate taxa. Hence, in habitats impacted by WWTPs, only a few tolerant macroinvertebrate taxa remain. These tolerant detritivore macroinvertebrate taxa play an important role in the degradation of organic matter, and biotic interactions between these taxa may either enhance or reduce the rate of sludge degradation. Therefore, the aim of the present study was to examine if the interaction between asellids and tubificids, both highly abundant in systems impacted by WWTP effluent, enhances the degradation of sludge. To this end, growth and reproduction of both taxa, sludge degradation and nutrient concentrations in the overlying water were measured in a 28-day laboratory experiment, subjecting WWTP sludge to 4 treatments: a control without macroinvertebrates, a tubificid, an asellid, and an asellid + tubificid treatment. Sludge degradation, phosphate concentration in the overlying water and asellid reproduction were enhanced when asellids and tubificids were jointly present, whereas tubificid growth and reproduction were hampered in comparison to the tubificid treatment. Hence, our results suggest that the biotic interactions between these tolerant detritivores stimulate sludge degradation, and thus possibly mitigating the negative impacts of WWTP-derived sludge particles on the benthic environment.

Continuous aerobic granular sludge plants: Better settling versus diffusion limitation

The application of aerobic granular sludge in continuous wastewater treatment plants is receiving increased attention. The introduction of better settling sludge in existing installations is expected to increase the plant’s treatment capacity by allowing a higher biomass concentration in the reactor. A lot of recent research has therefore focused on how to get stable granules in a continuous flow plant, which make up the majority of current infrastructure. Still, the effect of aerobic granular sludge on the treatment capacity and energy requirements has not thoroughly been studied so far and is not that straightforward. While it is clear that the introduction of aerobic granular sludge will result in better settling, it will also bring about a higher diffusion limitation – which is often overlooked. This study scrutinized the effect of better settling versus diffusion limitation in a typical continuous activated sludge plant (predenitrification type) through a simulation study. When only considering the improved settling velocity, the treatment capacity increased by 40% compared to conventional activated sludge. However, diffusion limitation could almost totally counteract the positive effect of better settling for a non-improved continuous system. The continuous system could be improved for aerobic granular sludge by increasing the aerobic reactor volume fraction, while lowering the oxygen set-point to benefit from simultaneous nitrification–denitrification. The optimization led to a 20% improvement in treatment capacity and a 10% reduced energy consumption compared to a conventional activated sludge system. Overall, the performance of continuous wastewater treatment plants could indeed benefit from the excellent settling properties of aerobic granular sludge, as long as process operation was improved in order to take into account diffusion limitation.

Fluorine Mass Balance Analysis of Effluent and Sludge from Nordic Countries

Recent publications have highlighted the ubiquitous presence of unidentified organofluorine compounds, whose environmental occurrence is poorly understood. In this study, wastewater treatment plant (WWTP) effluent and sludge samples from seven countries were analyzed for extractable organofluorine (EOF) and target PFAS, to evaluate which compounds are released back into the environment. Fluorine mass balance analysis of effluent samples (n = 14) revealed that on average 90% of the EOF could not be explained by the 73 PFAS monitored in this investigation. The levels of EOF in effluent (324–1460 ng of F/L) and sludge (39–210 ng of F/g of dry weight) indicate that a substantial amount of organofluorine compounds is released back into nature. A commonly overlooked PFAS class, ultra-short-chain PFCAs, accounted for 4% of EOF on average, while the remaining 71 compounds explained only a further 6% of EOF on average. The highest number of PFAS was detected in the effluent dissolved phase (37), compared to 29 and 23 PFAS in sludge and effluent particulate phase, respectively. The increased concentrations of EOF in both WWTP effluent and sludge are of concern, as the chemical species contained therein remain largely unknown, and thus, their potential health and environmental risks cannot be assessed.

Potential for Generation of Electrical Energy from Biogas Produced in the Anaerobic Treatment of Sewage Through Different Methodologies

This study aimed to evaluate the potential for electricity generating of biogas from anaerobic digestion of sewage and sewage sludge in Wastewater Treatment Plants (WWTPs) in the state of Minas Gerais, Brazil. Four different methodologies for determining the volume of biogas produced were considered. Estimates of biogas production used actual data of the volume of treated sewage and population reached by this WWTP with sewage as presented in a report by the local authority. The results indicate some discrepancies between the methodologies employed, but in general, they all suggest a potential of electric power generation at the same order of magnitude. The most divergent results were those in which the methodologies were applied to municipalities with a population of over 250,000 inhabitants.

Effect of the ozonation pretreatment on biogas production from waste activated sludge of tehran wastewater treatment plant

In this study, the ozonation impact on anaerobic digestion of wasted thickened activated sludge of Tehran wastewater treatment plant has been investigated. Regarding that, the thickened activated sludge, a final solid waste of treatment plants, was subjected to ozonation pretreatment to evaluate its characteristics. Three major sludge characteristics were considered for investigating ozonation effects on anaerobic digestion. A comparison of two different ozone doses, i.e., 0.05 and 0.1 gO3 g−1TS was performed for short-term (10 days) and long-term (30 days) sludge retention times. Furthermore, biogas production, sludge composition, dewaterability, and energy balancing, were studied during the periods mentioned above. The results show that the lower ozone dose has an acceptable performance in a short-term operation for all parameters except energy balance which was negative in all the scenarios. Higher ozone dosage not only decreased biogas production and volatile solids reduction but also significantly increased the energy demand of the system. In addition, a longer retention time reduced the effectiveness of the ozone pretreatment during that time. Eventually, the feasibility of ozone pretreatment capacity for sustainable management of different sludge from economic and technological perspectives can be evaluated by further assessing this case study.

Heavy Metal Potential of Domestic Biological Wastewater Treatment Plant Sludge

The use of sludge as fertilizers helps to the recycling of nutrients to the environment due to its beginning from wastewater and therefore relatively high content of nutrients and organic matter. However, wastewater does also contain hazardous compounds like heavy metals and micro pollutants which eventually are separated to the sludge during the treatment processes at the wastewater treatment plant. In order to improve the sludge quality, source tracking is a relatively cheap and effective way to find and eliminate hazardous compounds and prevent them from ending up in the sludge. The aim with this thesis was to investigate the fertilizer potential in sludge from wastewater treatment plant. The sludge is analyzed in terms of nutrient and heavy metal contents as well as physiochemical parameters. In order to determine the potential as fertilizer, the quality of the sludge is compared with other fertilizer alternatives, other sludge types and regulations for sludge use in agriculture. The work with sludge quality improvements in Gaborone is also investigated. Sludge from different stages along the treatment processes were collected in order to see differences in quality related to the treatment. The results shows that the samples of primary an aerobically treated sludge tend to have higher heavy metal content than the secondary sludge. The quality of the dry sludge samples indicates lower nutrient content than both the primary and secondary sludge, but similar heavy metal content. The analysis of dry sludge from indicates a low nutrient value and high heavy metal content in comparison to other selected fertilizer options and sludge from other. The processes for removal of nutrients from the wastewater are an important factor for the nutrient content in the sludge. Keywords wastewater; fertilizers; nutrients; sludge treatment