Sewage Treatment System

The job of the sewage treatment system is to collect gray drains from kitchen, showers, and wash basins plus black drains from toilets and combine them with washing drains.

From: Practical Engineering Management of Offshore Oil and Gas Platforms, 2016

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Systems and Equipment for Offshore Platform Design

Naeim Nouri Samie MSc Hydraulic Structures, in Practical Engineering Management of Offshore Oil and Gas Platforms, 2016

3.5.3 Sewage Treatment System

The job of the sewage treatment system is to collect gray drains from kitchen, showers, and wash basins plus black drains from toilets and combine them with washing drains. These are all classified as nonhazardous drains that do not contain oil or gas contents. The package then mixes and reduces the particles to small sizes. The main intention is to perform several tasks before discharging to sea:

Biochemical oxygen demand (BOD) of the system is reduced to a certain level (30–45 ppm). This will enable dumping to sea with no hazard to the environment. BOD is the amount of oxygen that microorganisms present in wastewater consume to decompose organic matter. It is measured for a span of 5 days in dark environment for 20°C water temperature. This is a measure of water purity. Drinking water may have a BOD of 1–2 ppm.

Reduce particle sizes to prevent piping clogging and at the same time enable their rapid disintegration after disposal to sea.

Discharge water is diluted enough to reduce total suspended solids to acceptable levels (30–50 ppm). Increased suspended solids limit water transparency and may impact fish breathing if trapped in their gills.

Disinfect the accumulation with sodium hypochlorite to enable its safe discharge to sea.

These are performed in several steps.

Black and gray water are mixed in a tank to have a uniform mix.

This mixture is disinfected with hypochlorite sodium to kill parasites.

The solids are fragmented to small sizes.

This solution is diluted enough to acceptable limits with freshwater.

In living quarter platforms that have a large volume of sewage material, to dilute it to an acceptable limit a large volume of freshwater is required. The main portion of solids may be filtered. This is either burned in an incinerator or kept in another tank to be transported onshore via supply boats. The remaining materials will be discharged via sewage caisson to sea. In many platforms this is a nutrition point for fishes. It is normal to have fish colonies gathering around these points.

Tanks can be made of mild carbon steel. Only hypochlorite tank shall be of suitable material such as plastic or GRP to prevent corrosion.

A macerator will disintegrate solids to a smaller size before being diluted with freshwater. Therefore it shall have a hardened surface to resist wearing of its internal surfaces.

Package capacity depends on the number of personnel on the platform. For unmanned platforms that are only visited by a limited number of crew during maintenance, a minimum capacity will be specified. For others, 100 to 150 L/day for each crew may be used.

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Management of Estuaries and Coasts

M.S. Connor, ... A.C. Rex, in Treatise on Estuarine and Coastal Science, 2011 Effluent Monitoring

The improvements to the sewage treatment system were specifically designed to address the pollutants of concern (Table 1). The pretreatment program has greatly reduced the levels of most of these contaminants in the sewage influent. Secondary treatment further reduces the concentrations of contaminants of concern, except for nutrients. DITP removes approximately 85–90% of the suspended solids and biochemical oxygen demand (BOD), 50–90% of the toxic chemicals, and about 15% of the nitrogen from the influent (Delaney and Rex, 2007; Delaney, 2009).

Table 1. Relationship of MWRA required actions to environmental improvements in Boston Harbor

Organic matter/dissolved oxygen Solids/ turbidity Nutrients Pathogens Oil and grease Toxic compounds Aesthetics
Pretreatment Low - - - Medium High -
Scum discharge ends - - - - High - High
Biosolids discharge ends High High Medium High Low High High
New primary plant High High Low High Low High Low
New secondary plant High High Low High Low High Low
New outfall High High High High - High High
CSO plan Low Low Low High Low Low High

Almost all the DITP flow now receives primary and secondary treatment, with a small amount of primary-only treated flow (blending) occurring during strong storms. Discharges of solids have declined as a result of this treatment, as have loads of toxic metals and organic compounds (Figures 8 and 9). Once used as a sewage tracer, silver is now only rarely detected in the effluent. Loads of organic contaminants have also declined. Only 3–4 lb of PCBs and 0.5–0.75 lb of chlorinated pesticides were discharged in 2008.

Figure 8. Annual solid discharges.

Figure 9. Annual metal discharges.

Reducing mercury in the environment has been a top priority not only for MWRA, but also for policymakers throughout New England and Canada. Mercury accumulation in fish is a major source to humans, and most water bodies in Massachusetts are subject to fish consumption advisories due to mercury. Through MWRA’s source-reduction program, approximately 75% of dentists in the region installed amalgam separators to reduce mercury inputs to the sewer system, and hospitals are reducing mercury discharges. Loads in the influent, effluent, and fertilizer pellets made from biosolids show large declines. Influent loads have been cut in half since 1999. Mercury discharges in the effluent have decreased from an average of 0.14 lb d−1 in 1999 to 0.03 lb d−1 in 2008. Now, most of the mercury entering Massachusetts water bodies originates from air pollution generated by power plants in the Midwest and Southeast.

Total nitrogen loads have remained about the same for several years, while the portion of the total load made up of ammonium has slightly increased (Figure 10). Nutrients are not effectively removed by secondary treatment, and the secondary treatment biological process changes.

Figure 10. Annual nitrogen discharges. Discharges of ammonium remained relatively high, a result of the secondary treatment process. (TKN, total Kjeldahl nitrogen, a measure of total nitrogen in the effluent).

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Sludge drying reed beds: A key ecotechnology for a sustainable sanitation infrastructure in Brazil

André Baxter Barreto, ... Breno Henrique Leite Cota, in Circular Economy and Sustainability, 2022

2.5 Sewage sludge: A challenge that needs to grow

The management and final disposal of biosolids from wastewater treatment processes is a growing concern in Brazil as sewage treatment systems are effectively implemented and operated. Planning the management of biosolids by providing forms of disposal that do not depend on landfills will be technically, environmentally, and economically necessary to enable universal sanitation.

There is no inventory on sludge management technologies in Brazil as detailed as ANA's surveys. But the most common alternatives are conventional drying beds for small and medium-sized WWTPs, and mechanical dewatering equipment (centrifuges, screw press, etc.) for medium and large WWTPs. Two other important applications are dewatering bags and alkaline stabilization. The destination of biosolids to landfills is still the main form of final disposal; however, there are important cases of agricultural disposal of sludge conducted by the state sanitation companies of São Paulo, Federal District, and Paraná (Sampaio, 2013).

Once sewage sludge is conventionally understood as an urban solid waste it is important to have an overview on the urban solid waste management infrastructure nationwide (Fig. 5). There are 2268 urban solid waste management units in the country, of which 70% are garbage dumps or controlled landfills, with only 607 sanitary landfills. Only 3% are composting plants for organic solid waste (Brasil, 2018a, b). These data show how insufficient the existing infrastructure is, especially considering that garbage dumps are the predominant form of destination. This scenario demonstrates the need to rethink the logistics of sewage sludge management by implementing the circular economy in sanitation.

Fig. 5. Number and type of solid waste plants by processing methods in Brazil (n = 2268).

Data elaborated from Brasil, 2018a. Diagnóstico do Manejo de Resíduos Sólidos Urbanos—2018. Ministério do Desenvolvimento Regional. (Accessed 19 March 2020).

Of the various alternatives for the proper disposal of sewage sludge, agricultural recycling is the most promising both from an environmental and an economic aspect, as it transforms waste into an important agricultural input. In 2010, some 42% of Europe's municipal sewage sludge was treated and used on farmland, 27% was incinerated, 14% was disposed of by landfilling, and about 17% was disposed of in other ways, according to Eurostat (Eurostat, 2015).

The economic benefits from recycling nutrients and organic matter from sludge should also be highlighted. Studies by Corrêa and Corrêa (2001) suggest that the nitrogen, phosphorus, and organic matter present in a ton of fresh sewage sludge can represent values in the order of R $ 22.00 per ton. These values can reach R$ 31.00 per ton and R$ 158.00 per ton for composted and thermally dried sludge, respectively.

Agricultural sludge recycling in Brazil is well established in some regions. SANEPAR, Paraná’s sanitation company, is the national leader, with a long history of research and practices. SABESP, from São Paulo, and CAESB, from the Federal District, are also companies with extensive experience. It is important to emphasize the established experiences with energy recovery from sludge in some larger treatment plants. Arrudas WWTP (Belo Horizonte—MG) and Belém WWTP (Curitiba—PR) are widely known cases.

But despite these important national experiences, there is still a huge demand for improvement and expansion, once sewage treatment infrastructure is expected to grow and traditional sludge management approaches face technical and economic barriers, given Brazilian geographic characteristics. Operational complexity and high CAPEX and OPEX make it difficult to use mechanized systems in small and medium-sized municipalities. Another important factor is the viability scale for some technologies, such as energy recovery and mechanical composting. These two approaches tend to be viable in larger municipalities, with populations over 100,000 inhabitants, once scalability and financial sustainability are linked not only to technical aspects, but also to market strategies. Finally, another limitation of landfill disposal, disregarding environmental aspects, is the scarcity of such structures, especially in small size municipalities.

Two other important regulatory frameworks are the National Solid Waste Policy (Brasil, 2010) and the National Climate Change Policy (Brasil, 2009a). Both public policies drive the sewage treatment sector toward better energy efficiency, reduction of operating costs, and improvements in sludge management. Thus, the Brazilian technological matrix requires approaches to sludge management that address these technical, economic, and environmental challenges. In this scenario, constructed wetlands systems are emerging with enormous potential to meet these demands.

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Groundwater Contamination

Charles R. Fitts, in Groundwater Science (Second Edition), 2013

11.2.2 Septic Systems

Septic systems for subsurface disposal of human wastewater are the rule in more rural areas not served by sewers and sewage treatment systems. Most septic systems serve a single household, but some larger systems serve a cluster of homes and/or offices.

A typical septic system starts in the series of drainpipes in a home's plumbing system. These all connect and drain to one pipe that runs outside to a buried septic tank, where solids settle and are trapped. The tank needs to be pumped out periodically to remove accumulated solids. From the tank, wastewater flows to a leaching field, usually a network of porous distribution pipes set in a porous material in the unsaturated zone (Figure 11.1).

Figure 11.1. Typical household septic system. The septic tank has baffles to trap solids and a vent for gases.

Wastewater contains dissolved organic compounds that fuel redox reactions in microbes that live in the system. Redox reactions in the tank are usually anaerobic, including fermentation, methane generation, and sulfate reduction (Wilhelm et al., 1994). The water leaving the tank has high concentrations of organic compounds, CO2, and ammonium (NH4+).

In the leaching field, oxygen is available and aerobic respiration and nitrification are the key processes (Table 10.13). The concentrations of organic compounds and NH4+ decrease, CO2 is evolved, and the nitrate (NO3) concentration increases. It is typical for effluent leaving the unsaturated zone of a properly functioning leaching field to have nitrate concentrations in the range of 20 to 70 mg/L (NO3–N: mass of nitrogen in nitrate per volume), which exceeds the U.S. drinking water maximum contaminant level (MCL) of 10 mg/L (NO3–N). In most septic systems, nitrate is a groundwater contaminant of concern. Some septic system designs include another anaerobic zone beyond the aerobic zone in the leaching field, where denitrification (Table 10.13) reduces nitrate concentrations in the effluent (Robertson and Cherry, 1995; Robertson et al., 2000).

It has recently come to light that wastewater effluent from commercial and household disposal systems can also contain a range of chemical compounds found in medications, food, personal care products, and household products (Kolpin et al., 2002; Standley et al., 2008). Chemicals in medications and food pass through humans and persist in the system effluent. For example, caffeine has been used as an indicator of septic system contamination (Seiler et al., 1999). Hormones are particularly troubling chemicals that persist long enough to migrate through the disposal system to groundwaters and surface waters, where they can harm aquatic life. In Cape Cod, Massachusetts, where over 85% of homes have septic systems, several ponds in the sand and gravel aquifer contained estrogenic hormones at concentrations approaching those known to induce physiological responses in fish (Standley et al., 2008).

Septic systems fail when the leaching field doesn't have enough access to oxygen to fully degrade the organic carbon with aerobic respiration. This can happen when the system is placed too close to the water table, in soils that are too fine grained, or in old systems that become clogged with a biological mat that remains saturated.

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Surfactants, Anionic and Nonionic

G.L. Kennedy, in Encyclopedia of Toxicology (Third Edition), 2014

Environmental Fate and Behavior

The use of surfactants in household, industrial, and institutional cleaning products mostly implies environmental emissions through the drain into wastewater treatment systems (sewage treatment plants or septic tank systems) and aquatic systems. The hydrocarbon chains of these materials generally tend to break down in the environment relatively quickly. The business end of the molecule behaves differently; hence, no overarching statements can be made. Sodium lauryl sulfate can readily be removed from aqueous systems (filtering and aeration) and is readily biodegraded (42 out of 45 Pseudomonas strains could degrade alkyl sulfates to saturated and unsaturated fatty acids). In sewage, sludge, seawater, and in selected organisms from 75 to 100%, degradation is reported for sodium lauryl sulfate. Several jurisdictions, including the US and the EU, have regulatory requirements regarding the biodegradability of surfactants.

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Chemical HRPs in wastewater

Gang Wu, ... Jinju Geng PhD, in High-Risk Pollutants in Wastewater, 2020

2.5.3 Migration and transformation of other HRPs in wastewater

DBPs are usually produced during the final process of disinfection of the water treatment, so the disinfection by-products generated are no longer discharged directly into the downstream water body through the sewage treatment system.

Generally, due to the non-biodegradability, nano-material cannot be degraded in sewage treatment system based biological treatment technology. Absorption is the main removal route for nano-material in wastewater treatment system. Kiser et al. (2009) investigated the removal and release of titanium in WWTPs and found that the sample containing 2250 mg/L TSS had approximately 85% for Ti.

Regarding microplastics, the overall microplastics removal efficiencies of WWTPs without tertiary treatment were above 88% and the number increased to over 97% in the WWTPs with tertiary treatment. The relatively high removal efficiency of microplastics by WWTPs indicated that most microplastics were retained in the sewage sludge (Sun et al., 2019).

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Biological HRPs in wastewater

Shuyu Jia, Xuxiang Zhang PhD, in High-Risk Pollutants in Wastewater, 2020 Medical and pharmaceutical wastewater

Medical and pharmaceutical wastewater contains a large amount of ARGs and ARB, which is the main source of ARGs and ARB in the water environment. Rodriguez-Mozaz et al. (2015) have detected ARGs in hospital sewage, urban sewage treatment system, and the receiving river in Spain, and found that the abundances of blaTEM, qnrS, sulI, and tet(W) in hospital sewage were higher than those in the urban sewage treatment system and the receiving river. ARGs within β-lactam (blaVIM and blaSHV), aminoglycosides (aacC2), chloramphenicol (catA1 and floR), macrolide–lincosamide–streptogramins (emrA and mefA), sulfonamide (sulI and sulII), and tetracycline (tet(A), tet(B), tet(C), tet(O), and tet(W)) associated with transposons have been found in Romanian hospital sewage (Szekeres et al., 2017). In addition, sulfonamide (sulI and sulII)), tetracycline (tet(O), tet(T), tet(M), tet(Q), and tet(W), β-lactam (blaOXA-1, blaOXA-2, and blaOXA-10), and macrolide (ermB) resistance genes were detected based on quantitative PCR analysis in typical pharmaceutical wastewater treatment systems (Zhai et al., 2016). The maximum concentrations of ARGs detected in the final effluents of pharmaceutical WWTPs were up to 3.68 × 106 copies/mL by Wang et al. (2015) and 2.36 × 107 copies/mL by Zhai et al. (2016), respectively, which were much higher than the concentration in MWTPs as revealed by Mao et al. (2015).

In hospital sewage in New Delhi, Lamba et al. (2017) have detected 748 extended-spectrum β-lactam resistant bacterial strains (including Escherichia coli, Klebsiella, and Pseudomonas putida) and 953 carbapenem-resistant Enterobacteriaceae strains (including Klebsiella pneumoniae, Pseudomonas putida, and Klebsiella pneumonia subsp. Pneumonia). ARB resistant to carbapenem also existed in hospital sewage in China, Croatia, and other countries in the world (Zhang et al., 2013a; Hrenovic et al., 2015).

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Stephen M. Mudge, Andrew S. Ball, in Environmental Forensics, 1964

3.9.4 Fluorescent Whitening Agents

In order to improve the optical (brightness) properties of textiles, fabrics are treated with a group of chemicals which absorb in the UV and emit in the blue end of the visible spectrum (Gilpin et al., 2003). After repeated washing, these chemicals gradually wash out of the fabric but they can be replaced by compounds added to washing powders. The major compounds are shown in Figure 3.9.2. As well as being present in washing powders, they are used in improving the optical properties of papers.

Figure 3.9.2. Structure of key fluorescent whitening agents (FWAs).

The quantities in use are (Poiger et al., 1999)

Whitening paper – FWA8 (7,600t · a−1, tonnes per year), FWA5 (100 t·a−1)

Textiles FWA8 (1200t·a−1)

Detergents FWA1 (3000t·a−1) & FWA5 (500t·a−1)

Washing powders contain between 0.03 and 0.3% of FWAs, notably FWA1 and FWA5. Between 5 and 80% of these compounds are discharged to the sewage treatment system. Therefore, these compounds will be present in the influent of domestic wastewater systems. Table 3.9.2 indicates the concentrations of these compounds as they pass through a typical STP.

Table 3.9.2. The Concentration of Selected Fluorescent Whiteners in Domestic Wastewaters (after Poiger, 1998)

FWA1 (μg·l−1) FWA5 (μg·l−1) FWA8 (μg·l−1)
Raw sewage 10 14 0.5
Primary effluent 6.9 10.6 0.018
Secondary effluent 2.4 6.4 0.024

Several studies have used FWAs as indicators of fecal contamination (Boving et al., 2004, Gilpin et al., 2002, Hayashi et al., 2002) and with other measures were successful in differentiating sources. Extraction Methodologies

Due to the relatively polar nature of these compounds, they are most likely to be found in the liquid phase and the most appropriate extraction will be using solid phase extraction (SPE) with C18 as the stationary phase in either columns or on disks (e.g. Poiger et al., 1996). Filtered water samples (~100 ml) should be passed through conditioned SPE columns and eluted with tetrabutylammonium hydrogen sulfate in methanol and finally water: dimethylformamide (1:1) mix. The eluted FWA agents can be quantified by adding a standard (an FWA not present in the system naturally) and determined by HPLC with fluorescence detection λex 350 nm and λem 430 nm.