Variables ambientales alrededor de las colonias de lobo marino

Human excreta contain high concentrations of microorganisms (10¹¹-10¹³ microorganisms per gram of faecal material) and are a vector of a wide range of disease-causing pathogens (Schonning and Stenstroem, 2004). Most pathogens are contained in the faeces fraction of human excreta and some of these pathogens are highly resistant, they can survive for many months in soil (e.g.

Ascaris eggs) (Feachem et al., 1983; Schonning and Stenstroem, 2004) as shown in Table 2-1. The survival of pathogens in soil depends on several factors such as the temperature, moisture content of the soil, soil type, vegetation present, exposure to UV as well as the method by which it was introduced (Jacobsen and Bech, 2012).

Table 2-2 Estimated survival times of pathogens during storage of faeces and in soil in days unless otherwise stated (norm. = normally) (from Schonning and

Stenstrom, 2004)

iAbsolute maximum for survival is possible during unusual circumstances such as at constantly low temperature or in well-protected conditions

iiData are missing for Giardia and Cryptosporidium; their cysts and oocysts might survive longer than the time given here for protozoa

All pathogens are sensitive to temperature; pathogens become deactivated and therefore harmless to human health above a certain temperature, variable between different microorganisms. Feachem et al. (1983) showed that there is a link between the temperature, time of exposure and pathogen deactivation and they developed correlations for most human pathogens present in waste water and human excreta, as illustrated in Figure 2-4. Pathogens can be inactivated by a short exposure to high temperatures but they will also be deactivated if they are subjected to lower temperatures for a longer period of time.

Figure 2-4 The "safety zone diagram" (Feachem et al., 1983)

Pathogen deactivation must be achieved by treatment before released to the environment to avoid risks of contamination and preserve human health.

Pathogens can be removed by biological, physical or chemical means. The level of pathogen reduction required depends on the end use that will be given to the FS with the highest level of removal required when FS is to be used in agriculture for horticultural crops (Kengne et al., 2014). It is also essential that the treatment process chosen is carried out accurately and until completion otherwise pathogen inactivation cannot be guaranteed. Germer et al. (2010) for instance show the importance of appropriate management of a composting process; an opened composting pile with material with an unbalanced C/N did not reach temperatures high enough for pathogen inactivation (<55^○C) whereas a pile with a balanced

mix of initial materials and additional insulation reached temperatures above 55^○C for 2 weeks which ensured pathogen inactivation.

Measuring pathogen content of wastes, the use of indicator organisms Testing for the presence of all pathogenic organisms to ensure satisfactory removal would be too time-consuming and expensive in practice given the wide range of microorganisms present. Instead certain organisms have been selected as indicator microorganisms, and their presence and concentration is representative of the pathogenic population present in the waste. Indicator microorganisms of pathogenic faecal contamination must meet certain criteria:

they have to be exclusively of faecal origin, be present in greater numbers than the pathogens of concern, be removed from faecal matter or wastewater in similar ways to pathogenic organisms and have clear and reliable ways of detection and enumeration (Mara, 2004).

In practice the indicator organisms of faecal material are coliform bacteria, helminths as well as bacteriophage as indicators of viruses. Coliform bacteria are pervasive in faeces and originate from the intestinal tract, their presence is therefore an indication of faecal contamination. There are tests that have been developed for the detection of total coliforms, faecal coliforms and E.coli, the latter having traditionally been used as the principal indicator of faecal contamination.

There are however issues with this indicator since other bacteria from the Escherichia genus can grow in the environment and sometimes can interfere with tests (Niwagaba et al., 2014). There is evidence that E.coli can be naturally present in the environment in tropical climates (Fujioka et al., 1998a;

Byappanahalli and Fujioka, 2004) and it is therefore argued that alternative indicator organisms are required. Clostridium perfringens can survive in water longer than other resistant enteric microorganisms and is therefore considered a suitable alternative indicator of faecal contamination (Medema et al., 1997; Sidhu and Toze, 2009).

Pathogens in FS are also present as viruses, protozoa and helminths. Aside from coliforms, the most common indicators of pathogen reduction are helminths given their high resistance and prevalence in LMIC. The helminth most commonly used

as an indicator is Ascaris lumbricoides because of the persistence and resistance to inactivation of its eggs. Ascaris eggs are the most resistant to treatment given their ability to survive in many environments and at a wide range of temperatures so a preferred method of measuring helminth inactivation is to determine the viability of the eggs present. Their detection involves the coproscopic method which applies a series of sedimentation, flotation, centrifugation and microscopic analyses (Moodley et al. 2008), making this detection method difficult to carry out in resource-limited environments.

Guidelines exist for the quality of treated human excreta required before their reuse, providing protocols for governments and organisations to follow worldwide and ensure reuse of excreta is realised in a safe manner (WHO, 2006). These guidelines however have limitations in certain environments and the pathogen limits set out by the WHO are not applicable worldwide. Limits for E.coli, Salmonella and helminth ova are set in the WHO guidelines for safe reuse of excreta. However, in tropical countries for instance coliforms are sometimes already present in soil from other sources than human faeces and are able to colonise the soil making them ineffective indicator organisms of faecal contamination. Fujioka et al. (1998) found that coliforms which are recommended as indicators of faecal contamination by the United States Environmental Protection Agency (USEPA) are naturally present in soil in Hawaii and Guam and their presence cannot therefore automatically be linked to faecal contamination.

Forslund et al. (2012) grew tomatoes by drip irrigation using wastewater and when measuring E. coli concentrations they found a weak correlation between E.

coli concentrations in wastewater and soil and no correlation between concentrations in wastewater and on tomatoes. According to the WHO guidelines, the practices used in the experiment were unsafe because of E.coli concentrations in the irrigation water above the recommended limits but their results show that the tomatoes obtained were safe for human consumption. This example showed limitations in the guidelines and the authors therefore called for a revision and improvement of the pathogen limits set by the WHO guidelines (Forslund et al., 2012).

The WHO guidelines establish pathogen concentration limits for the reuse of

excreta but there are no unified standard methods for the detection of pathogens in treated wastes, which is another challenge for demonstrating the safety of soil amendments derived from human waste and comparing them between different case studies. Sidhu and Toze (2009) highlight the need for standardised detection methods for pathogens in addition to standardised pathogen concentration limits in order to allow for comparable results between studies. The experiments carried out in this project used ISO standards for pathogen detection when available (ISO4832, 2006; ISO6579, 2012; ISO7937, 2004; ISO16649-2, 2001) or the most accepted detection methods in the sanitation sector when ISO standards did not exist (Moodley et al., 2008).

Heavy metals

Heavy metals are components present in sewage sludge that cause major concern because of their environmental pollution potential. Certain heavy metals such as Cd can enter the food chain through soil hence regulations set limits for final concentrations allowed in soil amendments derived from sludge. Heavy metals present in sewage sludge from centralised wastewater treatment plants originate mostly from industrial wastewaters and urban runoff (Sharma et al., 2017). Source-separated human excreta are unlikely to contain high concentrations of heavy metals besides those needed for functioning the human body. Cu, Cr, Ni and Zn are all essential elements for maintaining human health and are present in human excreta but are not in concentrations harmful to humans (BNF, 2018; Vinnerås et al., 2006). Vinnerås et al., (2006) characterised the sources of heavy metals from building blocks in Sweden that used urine-diverting toilets and found that grey water had significantly higher concentrations of heavy metals than urine and faeces. It is however not uncommon to find discarded solid wastes in OSS systems, especially in pit latrines with deep vaults (Niwagaba et al., 2014; Odey et al., 2017). These materials could be a source of heavy metal contamination of FS, especially if batteries have been discarded.

IWMI and Sandec (2002) for instance showed evidence of Pb contamination in composting piles, which probably originated from discarded batteries.

Contamination of sludge with solid wastes and potentially heavy metals less likely

to occur in CBS systems given that excreta are only containers are smaller and collected every few days.

Emerging pollutants

Human activities generate new types of pollutants, which often find their way into wastewaters and excreta. These are broadly classified as emerging contaminants and include anti-biotic resistant microorganisms, new synthetic compounds and organic contaminants. These components are new and hence knowledge of their properties, potential toxicity and effects and persistence in ecosystems is limited (Bolong et al., 2009). The presence of organic contaminants in biosolids for instance is increasingly a concern given that some of these have endocrine-disrupting properties but soil toxicity data of these compounds is limited and there is no consensus on their effect on human health (Smith, 2009; Verlichi et al., 2015, Thomaidi et al., 2016). New regulations and concentration limits for organic contaminants in biosolids are being developed to prevent negative health effects but the substances regulated and limits associated vary greatly between countries (Chang et al., 2009; Smith, 2009).

Smith (2009) argues that the concentration of organic contaminants has decreased in recent years due to more stringent regulations and technologically-advanced wastewater treatment mechanisms but also states that ongoing research, monitoring and assessment is needed for identifying new organic contaminants and evaluating their potential toxicity. After carrying out a risk-based analysis on the presence of emerging organic contaminants in biosolids from wastewater treatment plants in Greece, Thomaidi et al. (2016) also call for additional research to be carried out on the degradation and long-term fate of organic pollutants in the soil environment but also for stricter regulations of these compounds in the European Union, especially synthetic phenolic compounds (SPCs) and siloxanes (SLXs).

Similarly to heavy metals, most organic contaminants in wastewater originate from industries, household grey water and surface run-off (Smith, 2009).

Chemicals originating from personal care products (PCPs) and pharmaceuticals

are most likely to be present in human excreta and their fate during treatment and effect on soil are being researched.

Certain treatment methods can degrade emerging contaminants: Xia and Pillar (2003) analysed biosolids from 12 wastewater treatment plants and resulting composts and found that composting significantly reduced the concentration of 4-nonylphenol (4-NP), one of the most detected non-naturally occurring endocrine disruptor. Malmborg and Magner (2015) characterised the fate of 23 pharmaceutical residues during anaerobic digestion finding that the digestion process reduced the concentration of these organic substances by 30% on average. Complex analytical methods and equipment are currently required to detect organic pollutants since they are usually present in very low concentrations. Methods are being researched and developed to simplify analytical procedures, reduce analytical times and increase compound selectivity (Zuloaga et al., 2012; Dimpe and Nomngongo, 2016; Ferhi et al., 2016).